I Have A Lot Of Things To Say About Four - Tumblr Posts
I feel like Four was so persistent on wanted to keep the EXITors inside him forever is because he’s so attached to them, in a way. He wants to keep them because they’re really the only things from BFB he has left. I’m not really counting Post-Split contestants here because they most likely left to go live their lives or do something not BFDI-related.
Even if he tortures them with eternal math and abuses them, he still seeks their approval and wants to receive praise and respect. Why else would he make copies of the EXITors inside his mind during when he merged with the desert in late Post-Split? He could’ve chosen anyone else, but he chose the EXITors.
Alongside being possibly attached to them, he most likely also thinks of them as “lesser beings”, thus why he tortures them by doing math all day. He also probably wanted to suck up all 64 contestants, showing the extra classrooms. I’m assuming he wanted to keep them all inside him forever so he could always have them with him. Maybe make thousands of seasons, recreate S1 moments? I’m not sure, but that was most likely his motive.
TLDR; Four doesn’t want the EXITors to escape because he is so attached to them and he seeks great approval and respect from them.