For reasons of The Plague and other logistical things, I haven't been to many exhibitions in the last five years - just two Stafford ones, probably - but, it's very clear that model railways is, essentially, a retirement hobby now. You will see families with young kids, but they are largely just there 'to look' at the exhibits. I don't personally know anybody without a pension book who has a layout. There are a good few youngsters on here, though, which is encouraging.
Also, people, in the UK in particular, live in smaller houses filled with loads more 'other stuff' these days, and a layout of any size would be difficult.
Evolution happens.