While i agree that not ALL kids will like biking alone in all directions, I believe that a huge part of this isn't the kids themselves, but the environment they're raised in.
Raise a kid on acreage without electronics and internet and suddenly lo and behold, almost all of them will spontaneously go out and start exploring, and if they're all doing this they'll find and latch on to the other kids. And there's parks and playgrounds and church and sports and libraries and other places kids and families from wide areas tend to congregate.
And with all due respect: what is this idea of 'not a good friend match'? They're kids: they eat, sleep and play games. They're not professors or lawyers with 25 years of specialisation and gobbledygook talking past each other with their heads up their own arses about how important they are: unless they're violent and/or their family is dysfunctional, they're a good friend match. Isn't one of the first skills to teach a child the ability to negotiate, mediate, get along with others, irrespective of superficial differences or interests?
Raise children in an environment with on demand streaming, and multiple televisions in their homes and all their neighbour's homes, and hit them with games specifically based around quick dopamine boosts and vying for maximising engagement and attention spans, and with a parenting culture that says they have to be supervised and scheduled, and lo and behold, they act just like conditioned rats in psyche 101 experiments do.
And what is 'low-density'? Again, in my childhood, I moved INTO suburbia from a relatively less dense location. And I haven't even gotten started on the 'horrors' that happened where I lived when I was under 10. I'm in no way religious today (and back then, for context, it was the uniting church, which is barely religious by american standards), but we walked a few hundred metres to a neighbourhood house where an old couple lived and had church services and kids groups for the neighbourhood children: imagine the preposterous concept of 'not a good friend match' when you've got 10-20 kids in a several km radius. I had one friend a few hundred metres down the road. And I don't mean like 'one acceptable friend': i mean, there was a kid several hundred metres down the road. We just walked to each other's houses.
When the community got enough money together to build a church and community space out of cinder blocks, well then we walked a km down the road and back again.
To blame the things like 'kids don't like biking in all directions' or 'distance in suburbia' or 'not good friend match' as the causes or barriers to quality youth playtime? NO! Absolutely not! If anything, the very things that are being labelled as barriers are are the very ESSENCE of quality youth playtime and we wonder where its gone.
Quality youth playtime is BORN of isolation, independence, lack of supervision, self-direction, imagination, boredom, and danger.
The CAUSE of its decrease is not these things. Its not even necessarily technology: we still had TV and computers back in my day, but when you and everyone else have to wait a week between episodes of your favourite show (don't know what it was like in the US, there was no cable in my country), and you have to cycle 4-5kms over hilly terrain to get a book or a video or a game for a week and then return it, you did so (back in the day, our kids network also pirated pc games between us all, but that's another story).
Its universal supervision, scheduling, protection, anxiety, short-term rewards, emphasis on private vs public space, exclusion of children from public space, on-demand universal supply of media and entertainment, absolute abundance of convenience and the attention economy that's driving it.
The rest are just excuses to stop us having to deal with the actual issues. I'm no friend of suburbia, but suburbia itself does not negate quality youth playtime. And the idea that these things are the barriers or causes is somewhat comical to people who actually grow up with significantly greater levels of those things as actual barriers...and still have quality youth playtime.