The main reason for the block size limit is disk space. At 1MB, an attacker can force every generator to permanently store 53GB per year. At 10MB, an attacker can force every generator to permanently store 526GB per year. Even a small change in block size makes a big difference on the load that generators must bear. It must not be changed until the network is ready for it, and this time can not be predicted reliably.

If the block size limit is too high, an attacker can destroy the network by making it impossible for anyone to be a generator. If the block size is too low, fees get higher until the problem is fixed. Automatic adjustments would still carry the risk of adjusting to a limit that is too low.