I think it is more 'Ruby isn't sexy any more' because people older than 25 use it.

It's just the usual thing of the next generation not wanting to listen to the music the previous generation did.

These things come in cycles. I remember when 'Hot Java' was sexy and cool and only throwbacks wrote C. (And when C was sexy and cool and only throwbacks wrote COBOL, etc) There were lots of other languages and frameworks around at the time too that have long since been consigned to the history books.

I never thought fashion would be a factor in IT engineering, but you realise over time that the two things you cannot escape are fashion and politics. They are fundamentally part of the human condition.

If you want long lasting skills in the IT industry make sure you're good at fashion and politics. They'll take you all the way to a comfortable retirement.