Please learn about how consensus rules work.
"The consensus rules are the specific set of rules that all Bitcoin full nodes will unfailingly enforce when considering the validity of a block and its transactions. For example, the Bitcoin consensus rules require that blocks only create a certain number of bitcoins. If a block creates more bitcoins than is allowed, all full nodes will reject this block, even if every other node and miner in the world accepts it." [0]
Because users must consent to run full-node software with a particular version of consensus rules, miners cannot simply change the rules. This was shown in 2017 with Segwit2x and UASF(User Activated Soft Fork).[1]
In other words,
"If securing Bitcoin requires consensus on what Bitcoin is, and Bitcoin is a database of values assigned to keys, and Bitcoin has a protocol for reassignment of keys, then securing Bitcoin can only be done by … your node!" [2]
> [Miners] are the ones with all the capital to benefit from inflating the supply.
You're not thinking clearly about supply and demand. Because bitcoin has a fixed supply (21M), its price movement is a pure result of demand. If someone were to start inflating the supply, the price would drop, devaluing the coins for everyone including those doing the inflation because created coins are instantly visible to everyone. (Incidentally, this also creates a disincentive for Satoshi to ever move his "lost" 1M BTC. Moving them would instantly make them appear available to the market/network and be a massively inflationary event. Prices would immediately drop in response to this perceived increase in supply.)
> Unsure why you think the miners are just going to go home when it’s all mined and sell off their expensive equipment at firesale prices when they can collaborate to increase the amount of Bitcoin?
Miners work for the block reward (which halves every four years) but also for transaction fees (an auction in which you bid for blockspace for your transactions). The question for the distant future is: will transaction fees be sufficient to ensure the security of the network?
[0]: https://en.bitcoin.it/wiki/Consensus
[1]: https://bitcoinmagazine.com/articles/bitcoin-independence-da...
[2]: https://medium.com/bitcoinerrorlog/who-secures-bitcoin-95b19...