Speaking from the other side, but having been on your side for most of my 20s and 30s and felt exactly how you do, they probably do feel you detached from them.
Their lives fundamentally changed to the extent that as you say, any gathering necessarily must be on terms that allow them to parent.
And the level of last-minute cancellations and apologies increase.
And on top of that, they’re just not prioritising reaching out to you. Mainly because parenting occupies 25 hours of most days and they’re exhausted, but they’re also probably assuming that any activity in reach for them, like simply getting coffee at a playground while they try to make sure their kid doesn’t eat too much sand, is not your idea of a fun time.
So your outreach tapered down in response, but that is ultimately your choice.
The alternative requires you to quite selflessly keep up the outreach and be OK with a lower hit rate, and lean into the fact that you have far, far greater flexibility to meet on their terms than they do to meet on yours.
Not doing that is not an unreasonable choice, but they probably miss you and want you to be part of their kids lives.
Anyway, thanks for sharing this point of view. It’s a hard situation.
I think it's a fair response, and I can appreciate the truth in one's own life that leads you to write it. But this situation is a complex dynamic, no two situations are precisely the same either factually or subjectively. The same couple with a new child may stay close to one, drift away from another for totally different reasons that may not have one thing to do with intention or effort.
At any rate, I'm never too proud to reach out to old friends even if the time between attempts increases. Relationships may change again!