Baseball is defintely not dying but the market is getting more diverse. We are living in an individualistic society where people want to have a lot of choices and taylor their free time activities to their individual needs.
It is not like in the 1950s when kids only could choose between 2-3 things, now it is tons of different things whether it is parcour running, ultimate frisbee or whatever not even talking about electronic entertainment which is not starting to be a competitive sport too.
I think baseball will always be a top5 sport but we won't get back to a time when every kid does the same in his free time, society has become to individualistic and diverse for that.