CGt gets already millions of visitors per month and bucket loads of buyers, (https://www.similarweb.com/website/cgtrader.com#overview).
Some sellers just don’t get them and then believe they are not there.
Solution sounds simple but its indeed noting more then make something they want.
Looking at your offers I can tell you the soccer ball can be made faster then one can purchase it. Same for the pushpins. The clock has lots of competition looking better. Probably the school bus and farm house have most chances having its distinctive look. The other architectural models and fire arms, don't expect sales on those.
There are thousands of these models so if you keep making that type of models its going to be very hard time selling.
This is my honest opinion, I can be wrong about it but don't think so.
Best advice I can give you is train like hell and create distinctive items.