My honest opinion is this;
Being an Airline Pilot isnt all about flying for me.
If ALL I wanted to do was fly then I would join the RAF, or as like you mentioned consider flight instruction.
However I see the other areas of being an Airline Pilot as a real challenge and achievement such as;
Leadership; Captaincy
Business Leadership - Something I would look for mid-career
Teamworking, multi crew environment
Systems Management
Crew Management
Customer Relations
The list goes on....
And whats a bonus is the fact that you get such a variation in work patterns which I like and the scenery changes.
For me its probably 50% actual thrill of 'flying' the rest is my aspirations for leadership/management