Let's have lunch

In the last two years we have bumped into each other about four times. Every time we say "Let's meet up for lunch soon". And "Do you have my number?". Then we say "I think so, but if you have a card I might as well take one to be sure." Not so long ago I found a number of business cards from the same person.

The problem is not the number. I think we both know how to get hold of the other person. Why do we still play the let's-have-lunch-game when we clearly are not going to? It's probably because there is no quicker way to end an awkward greeting to someone you once used to know but have lost touch with. The polite way seems to be to suggest lunch. Which would be even more awkward. Which is probably why it never happens.