why do people bring their dogs to the dog park and then not watch them at all

I want to preface this by saying i know dog parks aren't for every dog and i know my dog has some reactivity. Marcus (my dog, not me, i know it's confusing) has been making really good progress. Vet-recommended trainer, lots of work, he's actually doing great in most situations now. I had been told the dog park was probably not the right environment for him, but after months of improvement i thought maybe a low-key morning visit would be okay.

It was fine for about ten minutes. Then a large dog came sprinting full speed directly at Marcus from across the park, completely ignored by the owner who was staring at their phone the entire time. Marcus went into full panic mode - barking, lunging, the whole thing. All that progress just gone in about 4 seconds. We had to leave immediately and he was anxious for the rest of the day.

The other owner looked up from their phone, shrugged, and said "oh he's friendly" as if that's relevant when my dog is mid-meltdown. I'm not even mad at the other dog, he was just doing dog stuff. I'm frustrated at myself for going, but also genuinely baffled at how some people treat dog parks like a drop-off daycare where they don't have to pay attention. How do you handle this? Do you just... avoid dog parks entirely with a reactive dog or is there a way to make it work?