Earlier quoted context omitted.
Check out Google Trends with XMPP
Can that predict the future? ;) I feel it's right that a protocol doesn't need to be in the general consciousness. See the even worse Google trend for SMTP, for example, despite email still being considered a growing network. I wrote a bit about protocols being for developers and not users at https://snikket.org/blog/products-vs-protocols/
Why didn't you look up Email instead of SMTP? It's not like you want to measure XMPP based on a XEP.
Protocols might not be for (end)users, but the underlying concept is - depending on what you want to build: A product or an open standard.
The protocol is important to users in the sense of devs.
An open standard requires users and devs.