It's comparatively smaller. When I go to stores, I see an entire wall dedicated to Gunpla, and yet a shelf or 2 dedicated to Patlabor. I'm not saying it's ridiculously smaller, because that's probably not the case. But if a a Gunpla kit gets 10 units made (let say each unit is a palette's worth), then chances are, a Macross or other series kit may only get 7-8 units on an initial run and let the market decide. But at the same time, Gunpla is comparatively small next to model cars or airplanes.
The thing about PG kits ARE that they're expensive. On average, I see more modified NG/HG and MG kits than I do PG kits. $30-75 USD is not as bad as $200+ USD. Plus you have to build the kit. So that's time and money to consider in the market.