A discount is similar to a tip. Tipping in America began in the old south when a slave belonging to somebody else did something for you. It was outside their normal duties so a gratuity was often given. It was, for example, standard that people left their shoes outside their bedroom doors in the expectation that they’d be put back polished. The tip was often in the shoe. I’d say given that history that tipping/gratuities and discounts are not generally a good thing. You don’t ask for a tip. It’s okay to accept one if it is offered.
History has moved on. Tipping is now expected in restaurants because the wait-staff is underpaid in the expectation that if they’re good they’ll make good tips. Even if they’re not good you’re EXPECTED to tip.
Discounts in the modern sense probably originate with Nixon’s wage and price freeze. That fundamentally changed pricing structures because they rolled back everybody’s product to the price it was on x date. If a company was running its product on that date as a loss leader then they might go out of business. Thus manufacturers started listing the suggested retail price, offering coupons and discounts based on one thing or another.
I always say to somebody in uniform “Thank you for your service.” If they were offended because I didn’t say it, that would be annoying. Likewise, to be offended because you can’t get a discount on somebody’s product is annoying.
Most pricing structures are carefully thought out. They take into account sometimes hundreds of variables. Most clerks are not empowered to vary the price even a little bit because some would abuse the privilege and hurt suppliers or their employers. There was quite brouhaha in my hometown when a clerk gave a couple of the local university football stars a discount. She got fired. But the local university jocks had come to expect discounts and it played badly before the university stepped in and forbid them from asking or accepting discounts.
It is easier to tell a client that a discount is no longer offered than to raise your prices. Some sort of psychology there, they are grateful for having gotten by cheaper than usual while they did, and are far less resistant to prices returning to "normal" when the discount expires than they would be to a price increase later after a price drop. It says your goods and/or services are really worth X, but you are/have been getting a deal at n% off.