The company reckons that homeowners are spooked by the way Theresa May's decision to call a snap general election backfired so spectacularly - and that this, combined with Brexit fears, is leading them to stick rather than sell.
"The property market was hoping for a downpour of new stock in June, but the Conservatives crawling over the line failed to deliver the injection of confidence the market needed, and put paid to any chance of a late spring bounce," says HouseSimple.com CEO Alex Gosling.
"Price growth has stalled, and sellers, it appears, are choosing to stay put, rather than accept marketing their properties at a lower price then they might have done a few months ago."
Of the 100 towns and cities that HouseSimple.com analysed, 81 saw property supply fall in June compared to May. Dundee and Barnsley registered the biggest drop-offs in property supply, down 48.1% and 39.3% last month.
London, though, bucked the trend, with property supply up 5.3% across the boroughs. Sutton stood out with new property listings in June up by 54.1% compared to May.
Lichfield and Hartlepool were the only other areas to register big gains, of 20.6% and 18.7% respectively.
Gosling believes that sellers may be being unwise by holding off from selling, and that if they're hoping for prices to go up again, that could be a long wait.
"If anything, homeowners should see this as a good climate to sell as long as they price correctly," he says.
"If prices have dropped where they live, they are likely to have dropped, possibly by even more, in the area they're planning to buy."
The biggest falls in new listings
Dundee, Scotland: -48.1%
Barnsley, South Yorkshire: -39.3%
Sunderland, North East: -25.2%
Torquay, South West: -25.1%
Hereford, West Midlands: -24.5%
Slough, South East: -23.8%
Hemel Hempstead, East: -22.1%
Bolton, North West: -21.5%
Ipswich, East: -21.1%
Rotherham, South Yorkshire: -20.6%
The biggest increases in new listings
Lichfield, West Midlands: 20.6%
Hartlepool, North East: 18.7%
Peterborough, East: 17.2%
Cambridge, East: 16.4%
Southampton, South East: 13.4%
Hull, East Yorkshire: 12.9%
Gateshead, North East: 12.3%
Aberdeen, Scotland: 12.1%
Warwick, West Midlands: 11.9%
Oldham, North West: 11.6%
10 most viewed homes
10 most viewed homes
This five-bedroom, £4.5 million property was built in 2009, and designed to impress - with an indoor pool, sweeping staircase, a state of the art kitchen, feature fireplaces, a gym, and a bathroom for each of the five bedrooms. It seems to have worked, as the property had 14,000 views in a month.
Did someone say footballer?
At the other end of the affordability spectrum, there’s a good chance that the attention this two-bedroom flat is getting (17,000 views in a month) has something to do with the fact that it costs just £113,000. In Newport that buys you two double bedrooms and an allocated parking space near the city centre.
This is a stunning home in Padstow, boasting six bedrooms, an impressive vaulted entrance hall, open-plan living, and an outdoor pool.
However, the most striking aspect of the property has to be the incredible views all around.
It'll set you back £2.25 million, but that hasn't put 20,000 people off viewing the property in a month.
For your £5.5 million, you get an impressive indoor gym and pool, plenty of entertaining space, a master bedroom suite complete with mirrored dressing room, and separate staff accommodation. The grounds are fitted with extensive security and CCTV, so nobody will ever get inside. While it's on the market, of course, we all get a chance to have a look around, and in one month 34,000 people have.
This beautiful four-bedroom house on the Isle of Skye is just £100,000, which makes it a reasonable proposition as a holiday cottage or bed and breakfast.
It has been recently renovated too, so you won't have a maintenance mountain to climb before you start. It’s a great place to view while you dream of a remote island life - which may be one of the reasons why 41,000 people have viewed it in a month
This six-bedroom newbuild looks fairly traditional from the outside, but inside has opted for a sea of shiny white flooring, a shiny white kitchen, and a master suite that comes with its own (shiny white) dressing room.
It’s well worth a look - after all 42,000 people have viewed it in a month - but if you want to move in, it’ll set you back £2.65 million.
This four bedroom detached new build in Grimsby comes with some footballer essentials - including a shiny white kitchen, Bi-fold doors onto the terrace, master bedroom suite with dressing room and a free-standing bath in the family bathroom.
And because it’s in Grimsby, all this comes with a very reasonable price tag of £379,000. It’s such a good deal that 58,000 people have viewed it in a month.
This new build in Cheam, in Surrey, is advertised without a price. But given it has six bedrooms, a swanky kitchen and bathrooms, a games room, several sitting rooms, and Bi-fold doors onto an impressive garden (built for entertaining ), you can safely assume you’re looking at several million pounds. You can have a look yourself, and decide what it’s worth, after-all, 92,000 people already have in the past month.
For the petrol head who moves in, there are also three reception rooms, five double bedrooms (four of which are en-suite and one of which comes with a dressing room). It’ll cost you £2 million, so take your time having a look first - joining 150,000 people who have nosed around in the past month.
This five bedroom detached home in Lanark is the most viewed property in the country, with 212,000 views in a month.
Clearly people are intrigued as to how they can get an immaculate detached five bedroom home for less than £200,000 - over £500,000 less than the average asking price for a five bed house in the UK. The answer is, of course, that Lanark is home to some incredibly affordable property - so this constitutes a pricey property for the area.