You’re right about that. Personally, I never understood how expensive tennis is when all you need is a racquet and a pair of shoes?Honestly, the Dock said it better than I will.
It's a process that has been evolving for years. The baseball landscape is much different now than a generation ago. I look at all the gear the players at my school are toting around in the spring, and I can see it as an immediate barrier to entry for poorer kids. They got their cleats, they got their gloves, some have not 1 but 2 bats, and they have a fancy bag to carry all the stuff in. Lord knows how much they paid for their sunglasses that look really good resting atop their baseball caps. Again, it's not on the level of financial outlay that golf or tennis is, but it's not like running where all you really need is a pair of shoes or basketball where all you really need is a ball and a pair of shoes.
Organization is not cheap. As baseball has become more organized, it has become more costly. Why is the organization deemed necessary? As population becomes more transient, people don't know their neighbors. If you don't know your neighbors, it's harder to round up enough kids to play ball. Organization is needed to bring the ballplayers together.
Also, where are you going to play in the inner city? Ballfields and old-fashioned greenspace in the inner-city has been disappearing for years, and a portion of the existing ones are poorly maintained or simply too dangerous to play on (broken glass everywhere). One vacant lot I played on as a kid was turned into a block of houses. Another where I played "home run derby" is now a parking lot. Different sport, but I think back to Tim Duncan. He was reportedly an excellent swimmer but had his swimming career come to a screeching halt after Hurricane Hugo destroyed the only pool available to him back in '89. Gotta have a place to do it.
Lastly, as the Dock stated, baseball isn't viewed as "a way out" for inner-city youth like it is in Latin America, or like soccer is in West Africa or running is in East Africa, or like cycling is in Europe (which is ironic because cycling is an expensive hobby in this country). In this country, basketball and to a lesser extent, football and track & field are the "way out" - the way to get to college, the way to maybe land a pro contract, etc.