A meaningless statement if you aren't going to introduce any points of comparison. But I would hardly call 735 conference participants a huge conference. Like, that's big but there are lot more then 735 theoretical physicists.

Claude tells me that there are about ~5000 theoretical high energy physicists actively publishing as tracked by INSPIRE-HEP (the de facto search engine in that field). If we estimate that about a third or half of string theorists take part in Strings in a given year -- because there are other big conferences like String Pheno that will be more relevant for many -- then we have something like 30-50% of high energy theorists working on string theory.

I agree that people should be "moving on to other things," but I'm not seeing the evidence that they actually are.