VN Vets not keeping contact was pretty much the norm for several of the excellent reasons posted.

A lot of units have associations with websites that often help guy link up.

"Together We served is a good site for this as well."

Some units with more cohesion, like Marines or SF tended to stay more in touch, if only through unit associations and reunions.

I belong to the SF association and attend a lot of functions. Just good to be around that type of people with shared unique experiences.
Next week there is a big ceremony at Ft Campbell where 5th Group is going back to the striped Beret Flash.
Looking forward to seeing a couple old team mates and guys I have gotten to know over some internet groups.
Last summer I met a couple team mates at the convention in Seattle. One was a WW2 Luftwaffe vet, still going strong.