Because – with a bit of practice – you can pretty much control your quad in the air and not having to run all over the place, a large flying field is not required.
You can stay stationery – well, give or take – and stay in control of your kite when flying. A lot less body language compared to dual line flying, where you have to move, some times run, up and down the field for speed control. With quads you can do it with your wrists! 😁
This way of flying opens up a whole lot of interesting places to fly. You don’t need that large and obstacle free field, but fly more or less wherever you like!