Why are there not more freelance testers out there?

This is a great idea! I was actually just recently looking for something like this, to help with testing on an app.

I think my only concern would be security with those who are testing your app, because you would most likely need them to test use cases by giving them special accounts and such. Is there some sort of checks and balances for people who are testers on the site? Can you make the testers sign a NDA before they test (if the project happen to still be in BETA or something)?

We've needed a crowd-sourced human testing platform for software products for some time.

It would need granularity: as a developer I should be able to purchase N minutes of time from N people, potentially in such and such a demographic.

It would need an API: I should be able to build human testing into my deployment infrastructure.

It would need accountability: at minimum I want webcam footage of the tester using my product.

There are complications, but I see no reason why almost all of these couldn't be overcome by sufficiently smart automation.

Someone go build this!

There's a bunch of those types of services which we are deliberately avoiding the approach of. It's really hard to know the quality of the testers behind it all, in addition to that they can raise bugs and give you an idea of what has been tested, but you doesn't give you an understanding of what hasn't been tested.

The time it takes to walk someone through all the use cases that need to be tested is not trivial. The reason for having a dedicated tester is so that knowledge of the system accumulates. I can't imagine how having to re-introduce your system to a new tester for every upcoming deployment could possibly be a realistic approach. In order for this to make sense I'd have to build a relationship with a freelance tester so that the same accumulation of knowledge could take place.

There's less demand for freelance testers because having a one is a nice to have rather than a must have.

Clients rarely understand the value of testers, they appear to simply be an optional additional cost. Freelance developers have little incentive to recommend them since it inevitably leads a smaller slice of client budget for them.

When an organisation gets to the stage at which it understands the value of, and develops a need for, a tester they probably have enough work and cash to occupy one full-time.