Yep, work colleagues are definitely not your friends. I left a job after 5 years some 15 years ago. My job was made redundant, and I was given a month's notice. There were 35 other employees there. I had no leaving party, no card with 35 names written in it, (or even a dozen!) no nothing. The Manager gave me a card saying 'best wishes' and a bunch of carnations from the petrol station across the road that cost £2.99. I did my last day, and most people didn't even wave goodbye. Never contacted me again.
Some others there got special treatment and a big party when they left, and some had big parties that 25 people from work went to when they were 25 or 30 or they'd have a hen party that 30-odd people would go to.... but once they'd left, I have to say, whilst a few kept in touch for some months, by the time they'd been gone a year, no-one was in contact any-more. So yes, it is common.
Out of every job I have ever had (I've had about 12 in my lifetime,) not ONE person has stayed in touch for long (if at all.) I have had 3 or 4 jobs where 1 or 2 people stayed in touch for 2-4 years, but they left the area, (or I did) or moved on into a different workplace themselves, and we lost touch.
I have also had 3 or 4 work colleagues in the past who have fucked me over and stabbed me in the back too. Made fuck-ups and arranged it so it looked like it was me who did it. (Or they stole my idea and presented it as their own.)
In previous workplaces (and my current one) we have socialised/do socialise a little, maybe 3-4 times a year, and they're all OK/were OK, but again, they would not stay in touch if I left.
I have just one very good friend who has stayed in touch from the past. And she is not an ex-work colleague ... From childhood. Known her 50 years. We see each other every 3-4 weeks, and have a very long history.
I have 4 other friends, (3 from my village, 1 from a hobby group.,) but we're not really close and they don't know much about me really, I just see them when I'm out, we socialise together maybe once a month, (at the pub or the village cafe in the parish hall,) and I see them when there's something going on in the little town not far from me. Sometimes chat for 10 minutes, sometimes grab a coffee, can depend on them in an emergency and so on, but not super close. I think if they or I left the village, we wouldn't stay in touch. My BFF of 50 years and I have stayed in touch through several house moves, and a number of job moves, and been there for each other through the deaths of our parents, and a number of other close family members, as we both know each others families.
But yeah, work colleagues...... Nah. They are NOT your friends.