> It gives miners complete control over the limit. They can make blocks of any size (within the current limit), thus triggering the conditions by which your proposal would raise the limit further.
There might be a long term incentive to keep increasing the blocksize, to further centralize the network (and kick smaller miners out), but it comes with the cost of losing out on transaction fees.
Miners have always needed to plan for the short term, I see no rational scenario where miners would spam their blocks with their own transactions (or low fee transactions) to keep increasing the blocksize limit.