I think both of those are good reasons, but there's also:
C. Web applications are the way most applications are used on desktop nowadays. The creator already needs to eat the cost of hosting the servers, so you might as well go for control and monetization over delving into making peer to peer work.
A. People do still come up with protocols. They've just moved up a level of abstraction. Why deal with the problems http already solves if you don't need to?
B. We now have big enough actors (corporations) that there is less incentive to unify, though even this isn't entirely clear cut. A lot of companies do seem to be trying to create standards for things like iot devices with some success