I think the majority of users here don't think baseball adds diversity because a majority of users here are European. But even then, the Netherlands and Italy have added to the global diversity in the last decade. Sorry, it's hugely popular in the Americas and East Asia, and even to an extent in Australia. But sure let's have water polo because 3 countries outside the Balkans play it. This isn't against water polo, I'm just saying there are tons of sports currently in the Olympics that are much less global than baseball, but their popularity in Europe ensures their continued inclusion. As I said, though, requiring a city like, say Paris, to build venues for baseball/softball is unreasonable. And as you say, the lack of professional involvement is another concern. Those are real issues, the sport itself not being global enough is not.
Talk about not being global, China has won 53% of the available medals since Table Tennis was added to the Olympics, with Korea winning another 18%. Only one other team has ever won a gold medal in the sport (Sweden in 1992). The only reason other countries have won medals in TT is bronze for the team event, where China and Korea can only win one each. That's just ridiculous. The same amount of countries have won golds in women's hockey since 1998 as in all TT events combined - men and women's singles, doubles and teams- in the same time period (one gold by South Korea in 2004 in men's singles). Think about that for a moment. I say this as someone who lives in East Asia and has witnessed the 'passion' for this sport first hand: Table Tennis has no place in the Olympic Games.