Because you have a limited amount of time to invest in certain things in life, and it's better to invest that time independently of your work environment. Not saying that you can't ever have it, just that some day will be your last day at wherever you are, and those relationships don't always follow you to your next job.
The fact that I have a limited amount of time to invest in things is exactly why those things are necessary to have at the workplace.
I like having fun, and I like making friends. Being limited on time, I want to maximize the percentage of time in my life that I spend having fun and I want to maximize the amount of opportunity I get to make friends. It's great that I have personal free time where I can do that, but why would I not also want 8 more hours per day at work where I can also have fun and make friends? It would be silly not to, that almost doubles the amount of opportunity I have to have fun/make friends!
>and those relationships don't always follow you to your next job.
See my other comment in this thread. I haven't found this to be the case. Sure, not every relationship follows you, but that doesn't mean I'm going to forgo the opportunity to cultivate relationships that will follow me to my next job, or even for the rest of my life.
And as I stated, things change as life goes on. I'm not telling you these things to piss on your parade. I'm giving you perspective that you clearly don't have yet.
Don't assume things about me, and don't condescend onto me like you're some wise master. I'm not some young fresh college grad. I've been around the block plenty, worked at plenty of companies, lived in multiple cities and countries, and seen my fair share of come-and-ago friends. Nothing about what I said changes.
I'm sorry that apparently you haven't been able to (or just haven't bothered to) build the relationships I have been able to, but work is unequivocally an indispensable part of how I (and many others) enjoy life and meet people. I absolutely wouldn't give up the friendships that I made at my workplaces for anything.