I've seen a lot of reasons here. But I think the top reason is so you don't quit.
One of the top reasons people stay at a job is they like their coworkers. We make friends and that costs the company nothing and it is worth so much to them. There's a dollar amount associated with you having a friend in the office.
Now your company lost this tool for keeping you without having to pay you more.
(I'm not saying don't make friends, be nice to your coworkers, we need it)