I suggest that causaility could be backwards in two of your arguments.
Users could use BTC for long term exchanges due to its low costs of carry long term. It is not that they try to lower the costs by holding, it would be just it is a better MoE (although not money) for that specific longer term exchange. Regarding those who especulate on BTC becoming a more stable SoV in the future, that's a completely different story, I don't think that those are trying to lower tx costs at all. It is a bet, an investment on its qualities to become a good SoV in the future.
Regarding the focal point argument, it could be that the market demands a fixed supply real asset, and it is the market who shapes BTC by ignoring forks not suited for what the market demands. No different than the decimal numeral system. The decimal system has 10 numerals because it is more useful for humans that way (binary, sexagesimal and hex are useful in other different contexts), the slight marginal difference that we have 10 fingers made it more useful than any other alternative for everyday human calculations.
It could be the same for the concept of fixed supply. It could be that the market sees no better monetary «policy» than a simple fixed supply, so if that is what the market demands, it will obviously reject any form of supply increase within BTC or outside BTC, the same way market rejected copper as gold in gold-copper alloys, despite kings trying again and again.