Some stuff can be silly prices, this stuff
for example costs £35 for three meters, not saying you have that fitted, but costs can easy mount up. And in the main one is looking at ½ day or a day, in real terms one could never do eight jobs a day, theory you should be able to do eight one hour jobs, but try timing your self going to do some shopping, no tools to unload, only popping in for a few items, and it's ½ day gone.
One can likely get 4 jobs a day with two guys, that's still ½ day a job, health and safety can't really do all jobs on ones own, even if second guy only a mate, and not an electrician.
If the work is brought to the tradesman, like taking car to garage yes can spend just ½ hour on a job, but when my son started as a sole trader he would always underestimate the time, in the main he would forget the time taken to write out invoices, write out estimates, and work out rest of paperwork, he would say I got £100 for 8 hours today (it was some time back) he would forget the 4 hours spent at home doing paperwork. Or going to the whole sale outlets to pick up parts.
One socket damaged, and a 15 mile return trip to get replacement, that's after hunting the van to see if you have a spare. In the main when he did get a couple of short jobs, he would then spend time twiddling his fingers, as next job booked for next day.