Maybe smartphones now do everything we need from them. In which case companies can seek to differentiate based on price, build quality, style, etc rather than some sort of feature arms race. A bit like most other things you buy in fact. Look at a small car - you have loads of choices but they are broadly similar. Some models target low price, some are way more expensive and focus on being a premium model, the rest sit somewhere in the middle.
Nothing wrong with Apple focusing on the premium end - the Fiat 500 - while other focus on attracting more techy users wanting to tweak their phone, or capturing the poorer end of the market.