They don’t of course, but sooner or later you are probably going to want to write, and written German can be a bit finicky about things like that.
However, once you have learned how to speak it correctly, rules like that are pretty easy to learn when you want to But I imagine, like me, even when writing casual English emails to friends, you like to use correct grammar, syntax, spelling, etc. You will want to do this also in German, especially to native speakers.
And you will find the capitalisation of nouns when reading, especially in complex sentences, immensely useful, I promise you. It’s true that some modern novelists ignore this rule: I suppose they are doing it for effect, or to differentiate themselves. But the majority don’t, and serious newspaper journalists don’t. (Conceivably headline writers might).
I believe that teenagers and students when writing online to their peers break all the rules, but I’ll bet they don’t when writing essays that they want a good mark for.