For one, you have to wear protective suits and respiratory gear, neither of which was really that effective. They really inhibited my ability to move so a lot of times I would just go gloves and mask. Second, you have to prep ground beneath with thicker than usual plastic sheets to catch the paint scrapings that fall down. This just doesn't really work that well and there isn't always an effective solution. People have bushes against the house most of the time and you can't really control where the paint falls so most of it just ends up on the ground and then gets cleaned up later.
The fines for avoiding regulation are extremely high but I never once saw an EPA person the entire summer and on the occasions where it might have been possible we were warned ahead of time. There is an unspoken agreement that you try to contain the lead paint but you can't really do that much about it.
The main difference that you notice about lead paint is the thickness of the paint. After main years it kind of "cakes", but also that it still looks relatively nice after a long time. In comparison to latex paint it just has a much nicer look and I can see why they used it.
Edit: as a response to other comments, it's relatively easy to detect lead paint, I could usually spot it when we showed up/based on the type of house. I don't know about other sources like pipes though.