Initially because I wanted a job that would give me time off to go windsurfing, along with sub-load travel to take me to far flung shores ( e.g Maui ) - and the money's not too bad - but it didn't quite pan out like that, though I do enjoy the flying.
..... and yes, sitting up the front with a nice cup of tea, whilst the rising sun turn the Alps pink sure beats the M25 rat race !.... to say nothing of the views of the Sahara, thunderstorms in Africa, flying to the Artic Circle, the vast expanse of the Russian Caucuses & Steppe, etc...... to say nothing of the great people you get to work with !