When I left my job and was gymless for a short period, I started running along the water in San Francisco after not having run for several years. Within two weeks, I was doing about ten miles. It's really hard to overestimate how much easier and more pleasant beautiful surroundings make walking and running. (Temperate weather 365 days a year doesn't hurt either).
Running barefoot outside---if you can either find a good place for it or the courage to declare your current place good enough, is a thing of joy.
(My current home, London, basically has temperate weather all year round. It doesn't really get cold here.)
Humans have sweat! We we're built for the heat! We can survive just fine in the arctic too. We're the most adaptable species on Earth.
You have to get in shape, but that's another issue...
For instance, in most places I've lived abroad I can walk for 5-7 minutes from my residence to a handful of places to eat lunch. In San Antonio, the closest restaurant (which I don't want to eat at for health reasons) is a 17 minute walk.
In other places I've lived when you're walking you are surrounded by something worth seeing, something interesting. Parks, interesting architecture, public artwork, other people, etc. In San Antonio, from where I live a walk would be nothing but highways, cookie cutter houses, and cookie cutter apartments for hours on foot before I got to see anything interesting. Prague for instance has a little bit of art in everything, which makes it interesting. Even the sidewalks themselves are patterned on opposing sides of the street and change between districts and sections to be artistic.
In other places I've lived for longer distances it's a simple and quick matter to access public transport on foot and then to continue on foot from where you get dropped off. In San Antonio, I'd need to walk 17 minutes to the nearest bus stop, then I have a long bus ride with multiple transfers to get to anywhere near a walkable part of the city from my residence.
These cities in the US are fundamentally built with cars in mind first and foremost, have almost no public transport, and have zero attempt to make them even remotely walkable. The weather is just a small piece. I could wear a hat and get over the heat since it's mostly dry heat here, but you can't get over the fact there's nothing to /do/ or /see/ or /get to/ on foot. Walking has no purpose here. I didn't walk everywhere just for my health when I was abroad, I did it because it was useful and efficient and fun.
The temperature changes at different times during the year, and during different individual days and months. So, how do temperature shifts affect the results with the place and people being the same?
Central America, Northern South America, Northern Africa, and the Middle East seem particularly bad.
Looking at the "walkability" graph, you see that a lot of the cities listed as the worst (Arlington, Forth Worth, San Antonio) are in Texas, where it's pretty hot.
Living in Las Vegas, I totally get this. You just don't go outside in the day time, which can put a crimp on activity.
On the flip side, in the winter it's very nice, and is the perfect time to go outside and get some exercise.