Look, if all you are interested it is money, sell drugs.
I do not use the travel benefits. I DO enjoy the work I do. I DO provide a service, and people appreciate that service.
Your question is better asked "why join the military?" After all, why would one want to get paid little to go in harm's way to protect people who don't appreciate my efforts?
Flying is what I do. I flew freight, and I flew patients. I fight to get paid a reasonable wage and have decent work rules. I do not expect to be a billionaire, but as a laborer, I want to make a living wage. Still, this is what I do.... what I was meant to do. If you need to ask why, then maybe you should not be in this industry. Maybe selling junk bonds is more suited to you.