In "To Kill a Mockingbird", why does Boo Radley stay inside all the time?
Boo Radley never explains this to the reader, so we have to make a few assumptions about why his character stays inside all the time. The assumed reason he stays inside also changes throughout the novel.
The first reason we hear that Boo Radley stays inside is that he is forced to stay inside, first by his father, and then by his brother, Nathan. Boo was labeled a "bad kid" when his was in school. He got caught up with the wrong crowd and his father chose to punish Boo himself by keeping Boo locked up inside the house so he wouldn't be able to make any trouble.
However, Jem comes to the conclusion after the trial and after witnessing the injustice and hypocrisy of the town that perhaps "Boo Radley wants to stay inside." Jem considers the idea that Boo can see what's going on in their town--the prejudices, the gossip, the hypocrisy, the judging--and, being a topic of much of the gossip and judgements, Boo chooses to stay inside rather than subject himself to that type of environment.
Boo has been forced to stay inside and he does understand what goes on in the world as much so he prefers to stay inside more. The decision soon becomes his that he does not want to interact much with the world because of this and is simply an isolate person. Because he is never seen to be out, the kids make a game of him pretending whether he is real or a myth. Atticus later talks to the kids of how you cannot understand someone unless you are in their shoes.
Boo stays inside his home due to the residents around him. He understands what occurs in the town and wishes to isolate himself from it. Boo's decision to stay inside is a choice made by himself.