I think that boils down to CAP theorem and whether or not you want to shift the problems onto the user. With collaborative tools like chat or shared document editing. It's far easier for the system to deal with and for the user to conceptualise an availability error like not being connected to the WiFi or the cloud provider being down for a moment. Than it would be to deal with consistency errors like conflict resolution and asynchronous communication, eg: high volume chat channels/threads where responses arrive out of order or too late to be relevant.

It's just easier to switch to a different tool like IM or phone when one cloud tool is down so you can quickly discus the topic there, that to postpone your mental train for when everything is eventual consistent. Or to switch to the 'offline' tools we already have, like e-mail, which require you to rethink your train of though to the different medium.

Also central authorization and authentication are not to be overlooked. Those problems also suffer heavily when partitioned.