For people saying when attending an MLB game, the game is not the main attraction, well, that's true for virtually every sport except maybe the NFL (don't attend many NFL games). They all have a million side attractions for the kids, bars and restaurants for the adults, blaring music, scoreboard cams, etc. People aren't in their seats. It's just the way sports are now, probably to justify the cost of the tickets. It doesn't mean baseball is failing.
I think attendance dropping is more a function of more teams than ever tanking. It's not new to baseball but it's more widespread than usual. Hard to motivate people to attend when the team isn't trying. The other sport with a lot of tanking, the NBA, is much more individual-star driven, so even if your local team sucks you can go see the Warriors, Rockets, Sixers, Lakers, etc. and see one of the other heavily hyped superstars play. Baseball, the way it works, you can go see Trout and he could easily go 0 for 4. It's unlikely you'll go see the Warriors and Curry will score 6 points (now he might rest that night, but that's another story). And even with all of that said, plenty of NBA games it looks like the first level is half-empty and they announce a sellout, or close to it...but those seats are owned by companies that only use them half the time.