Maybe it's because developers don't want to sacrifice Bitcoin's decentralization? By being conservative, BTC can remain the most secure and reliable cryptocurrency in the world. If you want to try out new features, use an altcoin instead. Adding new features into Bitcoin, will only make the network more complex. And this will make it less-secure over time.

I'd say Bitcoin will remain the "Linux" of crypto forever. ETH and the likes are the Windows/Mac of crypto. They will get shiny-new features, but will often experience "hiccups" along the way. As long as people are able to obtain true financial freedom, there should be nothing to worry about.