Yes, you could simply upload some code to the service, and they will be called only when there's a request to that particular code, instead of running a process continuously.
It's called "shared hosting" and was invented in the 90s.
It's fundamentally different than that. This is a discreet function as a single function call that is deployed with no other code that you have written. This allows deployments of individual functions without affecting the rest of the services. While possible before almost noone actually did that.
I disagree, it was a common pattern to have a single .php file for each page, independent from each other, which would receive input params (GET, POST and COOKIE), sometimes connect to the database, and do all the processing inline, outputting the result. The whole file was essentially an implicit function. The appearance of frameworks with a single entrypoint and which load models and controllers and such is fairly recent in the PHP world. When I started writing websites, already in the 2000s, this was how I first learned.
