Tradies don't get sick pay, holiday pay etc.
Most tradies can't work full-time into their 60s and 70s.
Tradies don't get employer contributions to a pension.
Tradies' rates include travel time, fuel, van, insurance, training, professional membership etc.
Tradies don't do 8 hours a day of 'paid' work - a typical working day will include assessing jobs, providing quotes, collecting materials etc. That's before we get into the general time commitment of running a business.
Tradies have no guaranteed work. Some days/weeks/months will be busy. Some will be dead.
And if they're injured or have a sick child or a bereavement etc. then they earn nothing.
My point is, if you're paying someone 75 quid for an hour's work (for example) that doesn't represent an hourly rate of £75. They might have to spend several hours on the road that day, a couple of hours pricing up jobs etc. So for an eight hour day, £75 might be all they actually make - and that's before all the business costs outlined above.
Personally, I like knowing exactly how much I'll earn each month, not having to do unpaid work, having a workplace pension, and having holiday and sick pay - that's why I'm not self employed.