pay
A few of things to mull over;
To pay for your instructors qualification in the UK will set you back about £50-60K with all the hours building, CPL exams, Instructors course etc.
To keep your licence ratings current on say 3 aircraft types will cost you around £1000-1500 a year.(that works out in earnings equivalent of about 40-50 trial lessons). One hour flying plus the brief and de-brief equals 2Hours of your time = £20/hr not £40
You have to do a minimum number of instructional hours each year to stay current or you will have to pay more to renew your rating.
All that money just to be able earn a living!!!!
Tell me one other profession that will cost you so much just to be in a position to do the job.
Most people/students are suprised when they learn how little we get out of the dual rate they pay to the flying schools.