Berkshire Hathaway why dont more people buy into it?

[QuarterTon]

Hi, I'm an investing n00b, i really know nothing about anything in this field. I've been doing as much reading as possible and it seems like bershire hathaway has produced something like 25% annual gains on average in the last 25 years... why dont more people buy into this? Do people not sell very often?

I realize the class A shares are like 120K per share but what about the class B shares that are about 1/30 the price (~4K)?