Heh, well the list price for Waves Horizon bundle is $3,999 and that's one vendor...
A lot of the plugins those users acquire over time are produced by individual devs or small Indy shops, who may not be around any more or inclined to develop Arm versions of older products. You'll find threads on gearslutz.com where some people aren't upgrading to Catalina because 32-bit plugins aren't supported any more.
I was referring to the "Intel-specific" part of your comment, not the price. I'm a professional composer and haven't ever come across an Intel-specific plugin -- loads of people use AMD. I think what you meant is x86-specific, but as other people have pointed out in this thread and others, it's expected that Apple will provide the ability to simply recompile for ARM. No big deal.