It's always been that way - certainly over the last 20 years. Another new 'the next big thing' every few months. Everyone jumps on the bandwagon, then the wheels come off leaving just a few diehard adherents to trundle on in obscurity...
To be fair, I don't think we can really accuse Mark Copplestone of this though. He's always been one who makes the things that interest him, when they interest him, and when he loses interest, he moves on. As I say, it's the artistic temperament. He has finished some massive ranges like DA for Foundry which he then went back to under his own brand. Some ranges (like the 1672 stuff) he clearly loses enthusiasm for partway through, and moves on. He seemed to stop sculpting altogether for several years, so personally I'm glad we're seeing new work from him at all.
It's a bit different to the 'new shiny' phenomenon, which is often driven by commercial interests and marketing.
But I do know what you mean. It can be a bit soul destroying