it all comes down to consensus and reaching it.
if the community is small, meaning it only consists of exchanges, a small number of nodes that are mostly run by miners-services-exchanges and wallets, then enforcing a hard fork is easy. you just inform that an update is on the way and release it, surely enough majority is a small number of people and they will change and cause a hard fork to happen easily.
but when community becomes big. meaning apart from miners and services and all that, a lot of users all around the world are running nodes, then it becomes very hard to reach a consensus.
this is why bitcoin has problem these days. also the first fork that bitcoin had happened fast and easy, granted it was a bug not an upgrade.
and in comparison altcoins fork away left and right easily because you just have to inform the small miners and the exchanges about the fork and you are on your way.
As I understand Ethereum, they have taken steps to mimic the deflationary nature of Bitcoin via the fixed rate of money supply, banking on a 1% annual rate of coins being lost.
i am not sure how exactly their plans are going to work but the max supply of ethereum is not even set yet.
there is no cap! and a lot of new coins are bing created each days.
and it is nowhere close to bitcoin.
bitcoin daily total reward is about 1800
BTCwhile ethereum total reward in one day is 27500 ETH (that is 15 times more)