I think some of them are just sticking to low fees if it's just their transactions. Besides, how often do miners transfer bitcoins to another address that artificially inflating the fee would affect all other users as well? Also, there is a possibility that the inflated fees from the miner might be taken by some other miner, so I don't think it's really efficient and clever to do it on their end.
There isn't much guarantees that the space that you're wasting in your blocks would actually result in larger than proportionate increase in the average fees as the miners have to consistently be inflating the fees with their own high paying transactions in their blocks. Since Bitcoin transactions are not that crucial when considering the time taken (as of now, since there isn't that many good use case for normal small value transactions), there are quite a few scenarios where users would wait for a bit for the fees to drop and thus the miners would probably have to wait for it to take effect.
I'm one of those small guys waiting a few hours before sending a transaction just to get the fees drop a little. While it's only a few sats at best, in the long run those small numbers would matter, especially now that we are already heading towards something bigger thanks to a few big companies that dipped their feet on the waters of bitcoin.
Also since most of my transactions aren't really time-sensitive and are mostly transfers to and from gambling platforms, waiting isn't even a hassle. Who knows, those few sats that I saved on a transaction fee might bring me a jackpot too lol.