Some data currently being published as web pages and sent over http is far more suited for being sent over MQTT.
So what happens to existing applications that publish over http.
Well IMO nothing as it is relatively easy to take this existing data and republish it over MQTT without having to modify the existing application.
Doing it this way would greatly reduce the load on the application server and reduce costs.
A while ago I developed both a python script and a node-red flow to do this if you haven’t seen the tutorial then here it is.