What you just said is also not true...
in my experience, (10 or more years of posting models) all of my models I ever put up for free always got downloaded no matter the standard. I have had profiles on Turbosquid here and many other places.
Whenever I put up a free model it always got free loaded.
On the other hand not all of my models have been bought. When I started out I also fell in the trap of giving things away for free or under cutting the market and selling things at 1 dollar but soon I realized that it does not pay off and it drives the value of 3D into the ground.
Also when you put your models up for free... as the 3D market of true buyers is so limited everyone hurries up to grab your models because no one really wants to pay for things unless they have to. If everyone has your models then why would they need to come to you unless they need something made from scratch?
That is the reason why free models are great to get you a job... they are like a calling card or sample so that a company will want to hire you to make more in their style if you meet their standards but it is terrible for online store owners who are trying to sell models consistently without having to make new ones all the time.
How many models have you sold 512pixel directly on CGT or other platforms? Somehow I doubt that you have clients paying you 50 to 100 dollars consistently every week. If you are able to make ends meet as a 3D modeler and online store and are making at least 25 k per year selling models I will shut up right now because you obviously know what you are doing.
In my experience though that is highly unlikely. Most people can barely sell one model every 2 or three months and those people are the best of the best. They are also able to sell models at higher prices like 300 to 500 range and so that kind of money if earned on a consistent basis can be considered a real job.
If you are doing well 512pixel it is probably because you are earning you keep working at a company or have established a personal clientele who knows you by name and you meet up with on a regular basis.