Is it weird nowadays to ask other parents about play dates?

Context: picking daughter (7) up from camp the other day, her and a friend she made there both run up to me with the "we want to have a play date! Can we please??" I ask a few questions and find it that other kid is about the same age, they don't go to the same school but were in the same karate class in the spring (dad took her so I never met other kid) they're ok with it not being today (we have plans for later) and other kid's mom will be here to pick her up in about 10 minutes.

I'm not in a hurry to get home so I tell other kid that we'll wait at the playground for her mom and maybe we can set something up for in a few weeks time. We end up waiting you 20 minutes before I tell my disappointed kid that we have to go. As we're leaving, we finally run into other kid and her mom in the parking lot.

It's clear she had no intention of seeking me out but now the kids have seen each other and demand play dates. Other mom gives me a glare, but since we're walking in the same direction I figured it wouldn't hurt to ask if they're planning on signing up for karate again. She again glares at me and says she doesn't know, so we just awkwardly leave.

I would write this off as a one-time encounter with a frazzled busy mom (she had 2 other kids with her and did look to be in a hurry), but this isn't the first time something like this has happened. I've tried to arrange things with friends my kid has made at dance, swimming, during meet the teacher night etc. I hear a lot of "Oh I don't know, we're pretty busy".

My daughter is a sweetie that other parents tell me their kids speak highly about. I don't think I'm being pushy, it's always instigated by the kids and I'll say something asking the lines of "they seem to have really hit it off, do you think we can set something up for them?" What gives? Are other families just too busy to let their kids make friends?