Replicas get more exposure and downloads because there are people who look for those certain planes/cars.

I’m also a fictional-plane-guy. The only reason is why is because I suck at making replicas (see my F-15) so I had to stay on fictional aircraft. I’m ok on those, but way below average as in building skill and detail.

People like replicas basically for the same reason they like sequels and reboots to movies. They like to see something that's familiar to them or something that's been pre-established in real life. It's almost like a sign of success to be a replica of something. While something that's fictional, while it can be more unique and intuitive, doesn't always have the same realistic vibe to it. It's kind of unfortunate, since I primarily build fictional aircraft as well, but it's true.

Oh. It does make sense. @ChaMikey

Replica

I second what @Delphinidae said. as for why replica gets more exposure is (imo) because people appreciate your attempt in creating something that flew irl, as for fictional planes, some people appreciate your builds, but some isnt as fond of it as you and other people are. Kinda like telling people history of a kingdom and telling a story of red riding hood. hope that makes sense!