Because no one else will give him more?
Like I said, a very similar player in Kevin Pillar only got about 1/2 of what Bradley is making. After this season, it actually is extremely likely Bradley will be looking at a much much lower salary.
It's not like he is going to struggle to put food on the table. He'll still be a very wealthy man (and living a dream for most of us). But he will certainly be a wealthy man making less money in 2021 in whatever city, which could be Boston. But probably not...