1. Facetime/Relationship building - If you're seen more and have better relationships, on average, you will get tapped for better jobs/projects more often than people who are in another state/country. If you are the only remote worker on your team then you are at a serious disadvantage relative to your non-remote team members who see your boss every day.
2. Ease of communication - Working from home, for me, is frustrating because when I want to walk over to someone and ask them a question or set up a physical meeting ASAP I can't. Phone calls and e-mails are great but there really is nothing like a physical meeting when it comes to hashing out problems on a white board or building a working relationship. This is also a negative because it can be very distracting to have people able to contact you any time you're at the office, but for me it is a net gain.
3. I love people. I love working with them and getting to know them and having conversations with my coworkers. This is very easy to do when you are collocated. For me, working at home is lonely.
4. Knowledge synergies - This almost falls under number 2. It is really nice to bounce ideas off people without having to stare at a chat screen waiting for a response. I really enjoy when my coworkers ask me a question and a discussion ensues between all of us about the best way to do things. This is easier than waiting for someone to type a response or getting everyone on the phone.
Many of these things are possible to do over slack or meeting up once a week but it really does not beat being in the office every day. Perhaps I am very career oriented but just #1 is enough for me to not want to work from home.