Personally I just like my colleagues so it's fun to be around them for the most part, and there are better lunch options around the office in my case (plus I'd never bother going somewhere when I'm home anyway). It being easier to just quickly ask a question is nice too. Also gets me actually out of the house and cycling for ~40 minutes a day. I also get way more done at work because working at the same pc I spend 90% of my free time at is not great at motivating my brain to do work.
Still, if I didn't have the option to just stay home when I don't feel like going to the office/am waiting for a package or something, I'd find that very annoying.