What is it about TS4 that makes a computer run so hot?

I have an older desktop, it does ok for most stuff. But when it comes to playing Sims 4, I have to have a fan sitting next to it to blow away the hot air coming off my computer. I've only recently had to start doing this. If I don't do this, my computer will overheat and shut down, besides that it would be very uncomfortable just sitting this close to it.
(I won't give my age, but let's just say I'm going through the change of life with hot flashes, so it makes it ten times worse).