Isn't that sort of like any job? You probably don't start off getting everything you want and when you're good enough, you renegotiate or go somewhere else.
Well, there's that. There's also the problem that most people are conflict averse when it comes to negotiation, that or they're just crap at it.
For guys who punch each other in the face for a living, a lot of these guys aren't the types to negotiate hard in a board room. Negotiating hard doesn't mean playing hard ball or screaming across a table, it means knowing how to frame your point of view in a way that convinces the person on the other side of the table that your perception of your own value is closer to reality than they initially perceived.
It's like negotiating the price of something when you go shopping. In the US and Canada, negotiating the price in a brick and mortar store isn't traditional. In other countries it's far more ingrained into the culture. Sure, we do it for cars and houses, but negotiating when you walk into a store at the mall is something that people typically don't do.
Personally, I'll go shopping and if I make any kind of significant purchase ($200-$500+ depending on the item), I'll ask to speak to the manager and negotiate. I'll ask about discounts for bulk purchases, or I'll offer to pay cash (they don't have to pay for merchant fees on cash vs credit card), or I'll point out that I can get a similar or better deal at another store and tell them that if they make me a good offer I'll buy stuff on the spot, or I'll talk about becoming a regular customer because I need to buy that sort of stuff regularly.
I don't always get a discount, but often I'll get 5-10% discounts or even more. However, most people just don't even want to ask.
The same applies to negotiating contracts. If you aren't comfortable negotiating, or come across as desperate, or can't explain to the other party why you deserve more than they're offering then you just won't get as good a deal.
Heck, I've been in jobs where a week after securing a significant deal or completing a project ahead of schedule or below budget for the company I'll ask for a meeting with my manager and I'll discuss the possibility of a raise. I'll start out with pointing out my quality of work, offer calculations of how much money I've generated/saved for the company, and then explain to them that it's only fair that if I'm producing more revenue for the company than my counterparts then it's only fair that I'm compensated appropriately, otherwise what would be my incentive to continue performing at that superior level?
I don't recall ever being refused a raise or improvement in benefits, time off, etc, etc. Of course, I wait until I feel I have a strong position to ask for those things.
The two biggest mistakes that people make when negotiating for better terms or a raise is that they either don't ask, or they wait until they're desperate (position of weakness). The best time to ask is when your perceived value is high. And it's always better to ask and be told 'no' than to not ask at all.