Do you mean US insurances company share how much they charge to there customer to other company ? In my country, they need to share driver file because there is a common system they need to fill but if we can have different rate from 1 company to another, they wouldn't share it......
Sharing prices would just bring down all the market.
If you work on a manufacturing shop that buy replacement parts, i understand you may want to know how much the panel builder pay for that to resale it to you. Then you will want to pay that lower price instead. This would be bad for the panel shop business
If you work for a panel builder, you may got better price for x brand because you use plenty but you will get higher prices for a brand Y that you buy just once in a while...
If i work for a competitor panel shop and even if i don't use much X brand you let me know how much you pay it, i may ask to get the same price as you. Then this will let me bid and probably win projects in some of your usual market even if you do good business there for decades.....This is just few exemples but there is plenty.