For me: price and weight. I frequently travel with my laptop, often with a single backpack or on a bike.
The Air is also way overkill. I had a 12" MacBook before that. It ran the software that I wrote. I write markdown in Sublime Text and run python scripts.
There just isn't a reason to get something beefier.
I could have probably gotten away with the air but there are times when it would be throttling with my uses. The extra io and other hardware upgrades are worth it imo. Especially the screen, its just bright enough on the pro to use the computer outside in full sunlight. I had a 2022 air at one point and that screen was just a bit too dim to use outside without finding shade.
