base to base distances are uniform. But the playing field dimensions aren't.
And if, say, by rule all baseball fields had to be a uniform size, a HR wouldn't necessarily be a HR the same everywhere. Balls that would leave the standard sized ballpark in Colorado or other higher elevation places would not leave parks in lower elevation/humid places.
You don't have to be a baseball purist to love the variation of baseball fields. Houston's hill and pole in CF may be a little much, no doubt, but the different dimensions and aesthetics of each stadium is great.