It seems to me sports these days have more of an issue drawing casual fans rather than one specific generation of fans (although this probably effects younger generations more since younger fans aren't as established in their viewing habits). Part of it is just the fact the media landscape is more fragmented and there are more entertainment options now so everyone isn't gathering to watch sporting events as much as they used to. As a result, there's less incentive for people who don't follow the sport as closely to go out of their way to watch, never mind pay for whatever cable/streaming package they need, since it's less of a communal thing people are talking about.
The other issue is the way the games are distributed and the high pricing of anything related to pro sports. New fans these days aren't flipping channels and happening upon games and organically becoming fans like they used since no one has cable. They also aren't going to pay $30 a month for the new NESN or whatever RSN streaming service just to follow a team or sport they don't already. Something like this new MLS deal (or the NHL's current situation with ESPN+ but without local blackouts) could be the future as it helps put the games in front of viewers who might not typically watch through apps they have anyways.