You are right, I hadn't considered that. Yet we're talking about established composers mostly, which also rely on famous soloist to get public. Chamber works sadly get less attention, as chamber music is seen by many as "background music". Since I am discovering chamber music myself in these days after years passed overlooking it, I cannot say if today's composers are as good as past ones in that genre. Also, of course, the difficulty to get the music performed is a huge problem.
But there are a lot of possibilities with technology. As I am approaching a little of composition myself, I discovered softwares, samplers to be more precise, which can allow to produce orchestral music with a good PC and a midi keyboard! The sound libraries get more realistic every year, now there are
super realistic ones like this, it's really like having an orchestra in your computer:
https://www.spitfireaudio.com/shop/a-z/spitfire-symphony-orchestra/ but as you can see the problem is the high price and the technologic competence required, but that would totally solve the problem of performance. Of course, real instruments are always better but technology give composers more opportunities.