They are closed because the industry is small, only so many deals to go around.
There is also a lot of corruption with shared deals. For example, my buddy get EPO (similar to pro deal, he doesn't work a shop but they gave him a 50% discount card essentially) he buy product, sells them below cost, makes a profit and the nearest shop looses money.
As a team, you have a better chance of selling. More people on more bikes riding more often and more places with a big jersey on each rider. You are one rider. Single riders need LOTS of exposure. And yes with luck and some skill an above average rider CAN get sponsored...its about EXPOSURE. Companies don't care if you can ride the best(much) but they do care if you represent them well and get them lots of magazine shots (winning races is an easy way to do this
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It isn't a bike companies job (not saying thats what you are saying) to offer you deals. Its your job to prove to them that a frame at 1/2 price once per year will be of value to them. That is a 1000$ / year investment. Will you, in return, get say 10X that much back to them. If you will, you might have a better chance of getting some bro deals
The more exposure the better the deals. The best pros get everything for free...the worst pros get percentage off of the product of the pro company.