Short Version: "Quality over quantity." It honestly doesn't matter how many commentary teams the Show implements, even if it's hypothetically all 30 broadcast teams, given that the same "blueprint" is used to script, record, piece together, and digitally trigger lines during the game, broadcast team 1 will sound just like broadcast team 2, team 3, and so forth if that original "blueprint" remains. It's a matter of getting the very first broadcast team to sound natural together before ever thinking about getting multiple booths.
Longer Version: I radio listen to more Oakland Athletics baseball games than I watch during the regular season, and I still love listening to the same Athletics announcer over and over again. If they were the only ones calling the playoffs and the world series, it would still be great because they sound magically great. The problem is not the number of people manning the booth, but the way the dialogue is spoken and strung together. Since MLB the Show sticks to the same "blueprint" on how to script, record, piece together, and digitally trigger lines during the game, that's the bigger concern on why commentary have sounded forever the way it does.
Even if it's hypothetically feasible for The Show to bring in all 30 broadcast teams (or simply more than one team), if The Show uses the current "blueprint" to capture, execute and implement commentary, commentary will still be the same and have the same recurring concerns.
Side remark: Example, the same goes with all their pitcher's pitching motion. They're using the same pitching "blueprint" from their first pitcher and most likely down to their last pitcher. Despite their best effort to "fix" their animation sequences this year, the same legacy concerns still arises because The Show is still using the same pitching "blueprint." I've been simply watching youtube footage of real life pitchers and MLB the Show pitchers and I finally noticed some major concerns on why the same pitching animation legacy concerns still exist (i.e. unnatural arm placements, missing the key "triangle" throwing motion, lack of tucking in the glove side arms resulting in a pterodactyl" effect, concurrent and unison torso and hip rotations, lack of independent hip rotation, missing anterior pelvic forward tilt, missing anterior angular front stretch and rear arm stretch, pitchers being too upright on follow through, etc.) I'll create a thread in the near future to address this concern with supporting graphics.