I would say the biggest reasons people don't do BIAB is batch size and their "setup."
I have an 11 gal Bayou Classics kettle and the biggest 5 gal batch I can do is about 17lbs, If I do that I have to hold out some water and "sparge" in a second kettle or bucket, to get up to my pre-boil volume. So, if I want to move up to bigger batches I either stick with lower ABV beers or change my setup. Can still do BIAB in a cooler, many do and it works just the same as in a kettle.
Some people also have equipment that was bought before BIAB caught on, few of us are going to let that equipment just sit around when it works perfectly well for us.
I think the other big one is one that Yooper pointed out, where they brew might no be conducive to BIAB, although I would debate with anybody about it being sloppy or messy, no more than what "conventional" brewing is.
If you're going to do BIAB you NEED a pulley to hoist the bag. I'm 35yrs old and 180lbs, can I lift a bag that started with 10-13lbs of grain and hold it for 15-20 min while it drains? Answer... yes I can if I had to, but to me it's just not smart, it's hot, sticky, heavy and awkward. If you want some back problems I'm sure this will help
. I rarely squeeze anymore either. I start brewing around 5:00AM, after filling the kettle and heating water to strike temps, it's usually around 5:30-5:45, so mash is done around 6:45 and I've only been awake for an hour and 45 min, I really don't feel like holding that much weight, let alone try to hold the bag and squeeze. In the past I would squeeze while the bag was suspended with a pulley, but have found that if I let it drain for 20-30 min I get the same amount of wort. I know some try to shave off as much time as they can, but I'm usually just getting breakfast around or may just use the time to cleanup the garage, so I'm not in a rush.