1) This doesn't seem to be a problem in literally any other major sport.
But more importantly:
2) Your statement isn't even true. Here are the past 10 World Series winning teams:
2020 - Dodgers
2019 - Nationals
2018 - Red Sox
2017 - Astros
2016 - Cubs
2015 - Royals
2014 - Giants
2013 - Red Sox
2012 - Giants
2011 - Cardinals
Only the Red Sox and Giants have won more than once, and you see a wide-range of completely different and unique teams. The last 7 winners have all been unique winners - this is FAR better parity than virtually every other major pro sport. Didn't the NBA boom into extreme popularity during a ~20-30 year period when the same team would win year after year (ie: the Bulls, and then the Lakers, then the Spurs dynasty, then the Heat and Warriors, etc)? The point is not only inaccurate, it's also illogical as evidenced by the fact that you see far LESS parity in all the sports that are more popular than baseball. Don't even get me started on soccer.