While I wouldn't have it any other way, I do think collaboration is pretty easy. I have multiple meetings a day with multiple teams and we have always been able to get projects completed.
There are so many collaboration tools out there and with modern, fast, Internet speeds, it's like you're in the same room as the other person.
Some issues I have noticed: Managers need to know how to manage remotely. When a manager can't manage remotely, it shows, and it's bad. A bad manager will just blame the employee (which happened to me).
Something else I noticed is that I am just not that close to my co-workers. While I have a social life outside of work. Many people use work as a social outlet and it can be very lonely working remotely.
I think this is all bullshit. It most likely has to do with rental contracts the company signed and not wanting it to go to waste.