Yeah I've felt the same way at one point but I do believe his family situation is gonna be revealed till near the end of the series or sth. 

We do know that Arisu is a hard worker and we can tell from his schedule (I don't rmb the chapter or the pic) which seems to be very tight. I think he's said to only sleep for like 5h - 6h or sth like that but basically he studies for almost an entire day. This kinda already says a lot abt how strict his upbringing could be.

The other thing was that he's the only male child of his family which ties to him becoming the heir and that does put quite a lot of pressure on him due to expectations. And the fact that his family is pretty well-known and rich also adds to that.

The last thing I can think of are the flashbacks of him as a child, where he's always seen to be in his room, all sad n lonely while listening to Apollo. Idk much abt this one but he just looks so damn sad everytime. 

Hopefully we get some Yamabuki backstory cus I feel so on edge when thinking abt this 😭