I see where you're coming from, but relationship need some amount of contact to survive.

Work forces you to be in contact, if the majority of your time is spent elsewhere due to changing job, or city, or gym, or having kids.. it's a blow.

I try to keep in touch with ex co-workers I cared about, but we live in different countries, at different stages in life, with different priorities, and it's hard to say the relationship is well.

That doesn't mean the relationships weren't built as they should, IMHO, they are just different kinds of relationships.