Generally speaking because it can be really,
really hard.
My dad described what it's like to hallucinate to me(He has an allergy that causes him to vividly hallucinate if he takes certain kinds of cold medication). Effectively, everything you see is real to all of your senses. And the hallucinations can get
intense. Like, you're sitting on the couch flying to mars intense. Or the person you're talking to is a giraffe intense. Yes, you
know it isn't real - though in some cases your mind will do everything it can to fool you into thinking it is - but it's still
incredibly distracting. You can brute force it, but in your head you will
always be screaming "you are a giraffe! Stop being a giraffe!"
Imagine after a while it would get very, very grating. And of course there is medication, but many of them have side effects that dull the senses and slow the mind, which isn't good either.