It's about trust. No matter what software you are running you always trust somebody. Intel, gcc, maintainers etc. You can't verify everything yourself. But one screw up can ruin somebody's reputation and then you can decide to trust somebody else. Well, with a client. Not with the protocol though.

Most people simply can't have deep understanding of Bitcoin internals. It would be terrible if Bitcoin would be driven by democracy in the way that protocol becomes what most people want (yeah, I'm not hoping for karma with this one). Because then it would become the same as politics. It would drop down to marketing and manipulating memes by some small minority optimizing for its profit.

The protocol is decided by miners who optimize for their profit and Bitcoin success is in their best interest because their earnings depend on it.