people are not ready to be in continuous collaboration mode, i.e. in the mode there they intensively, in real-time, generate worthy ideas and constructively receive(understand), analyze, improve upon and bounce back the ideas generated by the collaborating partner(s). It is very intensive brain activity requiring matching partners and it wears you off pretty quickly. It is like tennis - possible to do for a couple hours few times a week. Or like musical jam sessions - you can do it for prolonged times only when young, and usually with help of some "energizers".

It is one of the reasons why email is such a mainstay of collaboration.