A couple of reasons why it might be tough to draw a lot of hype and the casual fan to watch MLB games during the year:
1) April-June: this is the time when both the NHL Playoffs and NBA Playoffs are on. Here in Canada, do you think people in Toronto will care about the Jays in April/May when the Leafs and Raptors are making deep playoff runs? What about viewership across Canada when the Flames or Jets are on? Even in some parts of the US, especially in the north regions, baseball probably isn't that popular during April & May.
2) NFL starting up in September: for the most part, majority of MLB teams are out of it, and with the NFL season starting, likely the fanbases of those teams and casuals don't care anymore since its a lost season anyways. More casuals will tune into the NFL every Sunday.
3) There are 162 games over a full season and most of the games are really long in comparison to basketball or hockey. Baseball games likely last between 3-4 hours on average and for someone who is a casual fan, it could be a lot. NBA games are fast paced and there is always something happening. It's tough to get excited about a baseball game every night in comparison to games in the NBA. There seems to be more buildup to a regular season Lakers/Warriors game than there is for a Yankees/Red Sox series. Maybe because in the NBA those teams only face each other 3-4 times versus 18 times like in baseball.
4) The NBA is a star driven league: NBA teams only carry 12 players on the active roster and its not like everyone on the bench plays. In the NBA, one or two superstars can carry a team, where in baseball that doesn't work. So it's easier to promote guys like Steph Curry, LeBron, Giannis, Harden etc. We have even seen a player like Giannis carry his team, whereas in baseball that doesn't work. Just look at the Angels all these years with Mike Trout.
Casuals prefer going to baseball games only in the summer. It's an afternoon or night out with a group of friends. They don't even go to Blue Jays games to watch any of the game. More just to sit in the stands, get some sun, talk, drink beer and to take selfies. 2-3 games over the course of the summer are enough for these kind of people.