I totally understand your point, but Yeonmin has a different perspective. In the recent chapters, Yeonmin still doesn’t know that Taeseo is wealthy and a chaebol heir. To Yeonmin, he is simply a secretary at a well-known company. That’s why he tried to help as much as he can by doing groceries with his own saved money to support him a little and to show him his gratitude. Also, when Taeseo gave him the phone, he asked him if it wasn't too expensive, and then when he offered him the black card to buy whatever he wanted with, he felt guilty to accept it and said « this is the money Taeseo earned through his hard work, i also know how hard it is to make money, so it's hard for me to accept something like this » which literally confirm that Yeonmin doesn’t see him as a rich guy, but rather as a hardworking person
If my memory is getting that old well damn but I couldve sworn this was going well like what is this turn ? Why not just tell the guy what's going on like it genuinely cannot get any worse for you kid