Why do people get their PhD in science/biology?

This is in no way meant as an attack. I have my master's and would love to have a PhD, but I'm just not sold on the idea and I don't see how anyone would be. As a master's in biology, I can make about $70-90k/yr right out of the gate. Here's what happens if you go the PhD route: schooling for 6-8 years making ~$30k/yr working 40-80hrs/week; get out of school only to struggle to find a post-doctoral fellowship which is a task itself these days (make ~$40-60k/yr). After 4 years of post-doccin' (many people have to do 2 post docs), u may get lucky to get a $60-140k/yr (depending on the industry) or you may not. Nothings seems to be guaranteed with the PhD. The typical argument is "yea, well with a PhD I get to be my own boss and do the research I want to do!" Do you though? I mean, no matter where you go you still have a boss, and realistically, the research you can do is limited to what the people giving you grants say you can do. I love research as much as the next guy, but c'mon where's the incentive?!