Why not 'nosotros hablar español'?

Why not 'nosotros hablar español'?
 

I know the appropriate way to say 'We speak Spanish' is 'Hablamos español' but why not use the imperative form of the verb with the pronoun? I'm sorry if its a stupid doubt, but I'm just trying to improve my hold on grammar. Thanks :)

Hablar is the infinitive form, not the imperative. That aside, there are various possible "layers" of answer.

The simplest is "That's just the way it is". It might not seem very helpful, but it is at least honest.

A layer up from that would be "Spanish developed from Latin, and Latin used conjugation to indicate person, tense, and mood". I don't believe that linguists have traced back conjugation to its origins, so at some point this becomes "That's just the way it was - and the practice has been inherited".

Most languages conjugate verbs to greater or lesser degree. English does it a lot less than most (in part because it only has two tenses, and barely has more than one mood) probably because its origins as a creole led to simplification.

I meant infinitive, sorry!
And that's all right, that's the way it is sounds good enough for me. Gracias :)

You also conjugate verbs in English: "I speak" and "he speaks" do make a difference; you would never say "we speaks" or "she speak".
Spanish just has a bigger number of variations, as there is a specific conjugation for each person.