MLB had safety protocols. But teams did not play in a limited number of stadiums as you wrote, nor was there full isolation for players and staff. Following the Marlins outbreak, MLB did come up with stricter requirements. But outside of road trips, staff members and players were only "prohibited from visiting bars, lounges, malls, or other places in which larger groups of people gather" (source). That's nowhere near what the NBA was able to put in place.The MLB players and staff were supposed to be isolated during the season. Some of the outbreaks happened because of players who went partying outside the bubble. And there were enough outbreaks during the season that the schedule had to be significantly reworked several times, as in cancelling or postponing games so that teams with outbreaks would not potentially transit the v*r*s to other teams.
MLB has come closer to a bubble-like setup with the postseason, and there have been no cases so far (ETA: and none since August). So basically, your post in response to yeslek was inaccurate.
BTW, if I never hear the word "bubble" again in this context it would be too soon.