Because it was fun? Because I learned a lot about flying that way? Because I got to go all over the country flying a wide array of different and interesting equipment? Because I learned a bunch about myself? And honestly, not that many of the airplanes I got to fly were beat up POS's (though some certainly were). Also, the pay for this sort of work hasn't been terrible (in fact, until very recently, it was much better than entry level - or even 5 or 6 year - regional FO pay).
If I would have gone to RJ world, it probably would have been a better career move - but I certainly wouldn't have flown a PC12 to Adak, or out to gravel lodge strips on the Alaska Peninsula. I certainly wouldn't have explored Middleton Island on a four-wheeler for hours. I certainly wouldn't have learned the pleasantries in a nearly dead language, or helped bury a village elder. I certainly wouldn't have seen buffalo and reindeer from the slopes of Mt. Vsevidof, nor would I have watched Mt. Pavlov erupt in person. I doubt I'd have seen water spouts in a temperate rainforest or humpbacks bubblefeed around my old bosses broken down boat. I doubt I would have seen upside down mountains as I descended through an inversion over the interior, or sand dunes north of the arctic circle.
If I would have gone 121 out of the gate, I doubt I would have been able to do tours in Glacier Bay and Denali national park. If I would have made the "career" my priority, I doubt I would have been able to basically get paid to essentially not work (medevac) on Kauai for a couple years while my sons were little, and if I would have gone 121 I doubt I would have met my wife.
I mean honestly, if I had my choice, I'd go straight to a Legacy at 20 year pay and fly one trip a month, - but that's not possible. What I'm saying is that the things I personally would have had to give up to point my career in that direction are things I am not willing to part with. Of course, your mileage may vary - and in the pursuit of adventure there are quite a few aviators who've met their maker...but I wouldn't trade my adventures for any seniority number at any place - they make me part of who I am today (for better or worse).
Has it always been easy? Hell no - and frankly, I bitched mercilessly about many aspects of it (most notably the cold). I'm not generally considered to be a "religious man" but I will say that many of the things I've been fortunate enough to see as I've been flying "beat up little POS's" around North America have left me in awe at the majesty of the world; some of the experiences I have had have left me a fundamentally different person. While, yes, a solid and stable career is nice, I personally am glad that I got to have the adventures I did, and I'd absolutely recommend the "road less traveled" to any would-be aviator.