Let Bygones Be Bygones

I've been getting back in touch with some old friends and making new ones lately. Meetings typically fell into a routine that went something like this: relate current affairs, recent experiences and thoughts; ask about other friends, family members and mutual acquaintances; and finally, discuss the past. It took two persons in two separate occasions to point out that when I mentioned the past I was always bitching about something (and quite justifiably, some things that still have yet to change for the better). I felt a little embarrassed. I was whining about things I couldn't change; and whiners are never pleasant.

On the other hand, I must say, I'm just so glad I'm not bitching about the present. So why do you say, we let bygones be bygones?