People want to go to festivals with semi-(at least) acoustic music, but there are fewer people around doing mostly traditional music these days....so, they add in people doing singer-songwriter stuff and Electric Celtic and ...and...and the younger audiences don't understand the difference anyway.
Most everyone has a good time and the ads and signs are easier to make for *FOLK FESTIVAL** than for "Festival of mostly acoustic music from all over, with lots of up & coming kids who are trying to make it BIG with their own songs, and who owe a vague debt to Traditional music"

I know of several festivals where I can count on a reasonable % of tolerably 'folk/trad' music, but as organizers get old & tired, the newer ones just don't make the effort to distinguish anymore.

I KNOW that down in the hills of Appalachia, there are still local festivals which are 92.628% trad/folk, but I seldom get that far.

I have my records and memories.