because i do loads of them, and its usually the same thing each time (and a roll of 2c .75 is cheaper than 1mm 2 or 3 core, especially for the amount i use), just with varying numbers of lights. so i can wire them in bulk away from the job, get there, connect to existing wiring, either push connections into loft or move to a next to a light for future access, place wires ready for new ceiling and done. there also 230v so no problems with higher current
for other rooms, each job is usually different, so normally wired in 3c looping from one light to the next