These limitation exist because:
1. Coop has no timelimit. The more time server writes demo - the bigger it is. In result we're getting demosize limit exceed or even worse.
2. Editspam, mapfuck, entity spam messages - will make the demo grow faster.
3. A lot of other nuances like: newmaps, correct map state (sendmap/getmap), unsafe for performance stuff (lags, spam, and such mapfuck)