Why don't the developers just update Bitcoin like any other normal altcoin on the market?
For example give Bitcoin an update for larger block sizes, faster transactions speeds, privacy features, more transactions per second, lower fee's and maybe add in smart contracts.
All those things you've mentioned are already being developed. Expect for block increase, because bitcoin is going for of-chain solutions, that are far better than the on-chain solution that would make the coin to much centralized. Even the Director of Program Management from Microsoft stated that on-chain solutions (like block size increase) "generally degrades the decentralized state of the network and cannot reach the millions of transactions per second the system would generate at world-scale". The solution is on second layer solutions like the lightning network for example.
You can of course have a different opinion, that is up to you, but those are valid points and time will tell if BTC devs are doing the right thing or not. I actually think they are, and I continue saying that there is no other coin with the potencial of BTC. Maybe some coins are "ahead" in the sort term, but crypto are here for the future, and it's better for development to take it's time, so that the final project is good enough to stay in our lives.