As an American from the north east, one does not order more pizzas. One orders more pizza. More pizzas sounds like you do not understand what the food is.
"Mendas" is a present form of the verb "mendi" and as such it needs a subject. But there is no subject. It's only a question about ordering pizzas.
"Pluvas" means "(it) rains". There is no subject either, at least not it's not visible in Esperanto. Yet that's what you say, not "pluvi"
Yes, "pluvas" is the verb which doesn't have a subject. The reason is simple there is no subject. It just happens by itself. In English it is "It rains". But what is "it"?
I think because it's an answer after another sentence/question: "cxu vi volas mendi du picojn?"- "kial ne mendi pli da picoj?" "Do you want to order two pizzas?" - "why not order more pizzas?" At least, that makes sense (both grammarwise and ordering more pizzas is always a good idea)
After dozens of times of re-listening I still cannot determine what words are being said. Anyone else have that problem, where the entire sentence sounds like one long word?
Why is it assumed "you"? I used "we", since there are no pronouns and any instance with multiple pizzas sounds like a many-person event.