A season pass is $1400, but there's parking too, and park food is super expensive. He probably averaged 2-3 times a week for 20-30 years, so it's doable, but still expensive.
The question is, why? It's just corporate commercial media content. I can understand attending 3000 Dodgers games way easier. At least a baseball game at the ballpark is real. Disney is just cartoon characters made into costumes, average quality amusement park rides with extreme lines, and cheap, gaudy decor.
I had season passes for Six Flags for a couple of years when my family was young, but we stopped renewing because we had already done it all repeatedly. After that we went once or twice a year, and sometimes skipped a year. We did have a lot of fun the years we had the passes.
I think Six Flags is better than Disney because the rides are better. Disney is focused on exploiting their IP, and the rides are just average.