The maximum block size must be continuously adjusted to keep the transaction prices stable. The only way to change the maximum block size is through a lengthy political process of debate, decree, network fragmentation and majority agreement.
This is a bad idea. The generators will collude to keep the block size small; transactions scarce, gouging the market.
Some may try. Keep in mind that generators have no sustainable monopolies on generation, not even as a group. If the major generators collude to keep block sizes small amongst themselves; say by keeping their own max block sizes at 1 meg, but the regular users' clients all have a max block size limit of 3 megs, then the rising backlog of lower fee transactions will attract new players into generation. Maybe forcing the colluding generators to change, maybe not, but a natural price balance will be maintained. Perhaps the occasional blockchain split fight is neccessary.