Obviously that doesn't stop people from moving there but I am always shocked more walk-able dense development hasn't taken root.
Because it inevitably butts up against people’s desire to not live near lower socioeconomic classes who may not be able to afford a car centric life. See the prevalence of school rankings (proxy for parental wealth) in real estate websites.
Older cities or older areas within cities with dense construction were grandfathered in, but I doubt we’ll see another new city like that in the US. The primary way we separate us from them is with unwalkable distances.
The flip side to that is sprawl is cheap living. SF doesn't sprawl but that means you can't afford a house unless you're rich.
One key, in my suburb area there's reasonably sized community parks all over. Shortly I'll take a 30 minute after-lunch walk, at the park that's a few houses down and big enough for a 30-minute walking loop.
Commute times CAN be long, but don't have to be. I have no idea why motorcycles aren't more used, especially in areas where there's no real winter. In CA you can lane split and _really_ cut down commute times. Here in AZ motorcyclists can't yet split lanes, but we can use the HOV lane. Cuts my commute time in half.
Further, Phoenix doesn't have a great downtown area anyway. There's plenty of interesting restaurants and shops spread throughout the valley. I just don't have to go "across town" very often, so the sprawl isn't that big of a deal.
Lastly, I can be in downtown Scottsdale in 30 minutes if I want, but I can also be in alone in nature, with likely no one around me for miles, in about 45.
As a motorcycle rider myself, I think you simply don't understand how bad it gets in ATL (both during summer and winter).
I currently live in Seattle, and it rains quite often, but it is just a drizzle most of the time, and I can still ride quite comfortably. Summer is a bit too hot at times, but nothing wild. Winters are fine too, aside from those very rare snow days.
Before moving to Seattle, I used to live in ATL, and I can tell you I would never ride a motorcycle there for multiple reasons.
1. It doesn't rain as often in ATL as it does in Seattle, but when it does, it comes out of nowhere and it pours buckets. Impossible to ride, even driving a car feels extremely risky with those rains.
2. Winters in ATL tend to be colder than in Seattle a lot of times (not averaged out, but on a day-to-day basis; e.g., one day in January you wear a winter coat, a week after you wear shorts and a tshirt, and another week later you are back to your winter coat), and summers are always much much hotter and much more humid. Weather swings much stronger in both directions. Humidity is a total killer. Riding in ATL during summer is pretty much impossible, unless you invest into cooling solutions (like cooling vests and such, which barely work for longer than 20 minutes at a time, as I found out from my own experience). You mention Phoenix, but the crucial difference is that air in Phoenix is very dry, which is much better for riding (or being outside in general). I witnessed 95F+ temps in Seattle (which also has dry air) a few times, and didn't even blink an eye and was able to stay comfortably outside. In ATL, I couldn't stand being outside even for a few mins once the temps climbed above 75F. Overall, I would say ATL has way way less rideable days than Seattle, and that's despite the Seattle rain.
3. Last, but not the least, drivers. While this isn't the main factor in my decision to never ride in ATL, it could be for a lot of people. Drivers are very aggressive, with many coming from very rural or suburban GA, driving giant trucks and having some animosity towards motorcycle riders specifically. I am not joking about the last one, I legitimately heard multiple people claim they wished it was legal to hit motorcycle riders on the road. But again, this point is just a minor one for me, as it is much more subjective than the first two and can be just written off as my personal experience aka anecdata.
With that in mind, I just want to say that this is not my critique of ATL as a city overall, just when it comes to riding a motorcycle there. If ATL manages to get the career opportunities for devs going with all those tech companies opening big offices there, and it all succeeds, I would consider moving back, despite the weather. ATL has quite a lot of things worthy of praise and appreciation that I miss while living in Seattle.