What does 'there's nothing to say that...' mean?
Other variants of this structure are
Nobody says you can't/have to...
It's nowhere written that you can't/have to...
They all mean that there may be a perceived mandate forcing certain action - but there actually isn't. It's just in your mind. And as soon as you realise this you enable yourself to make a free decision whether or not to go with the suggested course of action, do the opposite or yet something else entirely.