After being on this forum for a while I get the impression everyone is playing with several characters. Am I alone with only playing with one character?

Sometimes I hear people say "do another playthrough with another character". That also makes me a bit confused since I have been playing over 300 hours with just one character and I don't think I have even seen half of what the game has to offer yet. So how can people do several playtrhough? :S Am I missing something?

What is the appeal of starting over with different characters? Is it for roleplaying? Are everyone here roleplaying?

Also what is meant by roleplay I wonder? I have looked at some guides and videos for it and 50% of the time it seems to mean to play "in character" as in you maybe pick a role of hating elfs and play as such. And the other 50% it seems to mean having rules like eating 3 times a day and not quicktravel and so on.

I don't quicktravel anywhere, I don't use inventory in fights, I don't use wait (only beds) and I save very sparsly, does that mean I am roleplaying?