We have a female plumber but she openly admits she doesn't do the "heavy" work jobs like fitting big radiators or boiler replacements or bathroom fitting etc. She basically just does "light work" like changing taps, repairing leaks, fitting small radiators, GasSafe annual inspections, etc.
Yes, I know "some" women would be physically strong enough, but most aren't. Same with blokes really - you're not going to get a 5 foot nothing skinny wimpish bloke man-handling a 10 foot radiator on their own either!
Some jobs, like firefighting, now have hoists and lifts fitted to the appliances, wheels on heavy equipment, etc., so that being a "big burly bloke" is no longer a basic requirement.
Self employed tradies are different in that it's still basically men doing the "heavy lifting" kinds of work as there's no employer required to provide the equipment for making it safe (and accessible).
There is also an aspect that for some "burly blokes", the physical ability to lift heavy stuff is their ONLY skill, hence why they become labourers, scaffolders, roofers, etc., as they've not got the skill set for office work nor the more technical trades such as heating engineers or electricians.