There are several ways that miners could try to convince the Bitcoin community that a change to increase mining rewards would be beneficial.
- They could argue that the change would help to secure the network by providing a stronger incentive for miners to continue participating in the network.
- They could also argue that the change would help to increase the overall adoption and use of Bitcoin, which could lead to an increase in demand for the cryptocurrency and ultimately drive up its value.
If double spends looked imminent, or started occuring, I think it would make sense to fork to increase the block reward. Of course, bitcoin has forked before and it becomes a political issue. Personally, the big block wars (and subsequent Bitcoin Cash split) was where I got off the Bitcoin train.
But if a fork happened, and the network that didn't adopt the higher block reward started getting 51% attacked, I do think people would move over to the new network (and that would become "bitcoin")
This line of thinking is a fundamental misunderstanding of who holds the power to change the rules of a system like Bitcoin. It's not the miners, they just enforce the rules. Economic actors are the ones who agree on which rules miners enforce.
That hard fork the miners created? It's worthless, just like every other time miners have tried to change the rules.
Until It isn't.
Miners will one day decide to hardfork bitcoin to increases the mining rewards, hence increasing the supply. They will of course need to prepare the narrative, and say "it is for the good of bitcoin".
It might be in 10 years, or in 50 years. But on a long enough time-scale, you can be sure of one thing: Bitcoin will change, because it's man-made and because it's mutable/forkable.