Allowing a very large number of people to edit a document at the same time isn't trivial in terms of the state management and network load. Everyones edits have

Allowing a very large number of people to edit a document at the same time isn't trivial in terms of the state management and network load. Everyones edits have to be sync'd and sent to everyone else. Higher numbers than 100 are certainly achievable but perhaps there are limitations in their infrastructure for processing power available to a given sheet.