I really wish people would actually do at least a bit of research around licensing before they start carrying on about challenge policies and how unfair it all is and how ridiculous staff are being. It's not a God given right to sell or buy alcohol.
To have and keep a license you have to meet certain conditions, they are based in law, but also around being a responsible retailer of alcohol.
There are hefty concequences for the seller and the retailer if those conditions are not adhered to, fines, license restrictions or removal, and ultimately you can be imprisoned if the law is broken, however the law doesn't have to be broken to break a license condition, nor to not convince the licencing authority, trading standards or the police that you're not a responsible retailer.
To that end retailers need to prove they're sticking to the licence and also a responsible retailer. To do that they need proof, an ID log of all purchases that have required ID - and no they don't simply take your word for it if it's empty and you tell them that no one in the last 6 months has needed ID because they were all over 45.
Trading standards and licencing also use 'mystery shoppers' as do retailers themselves (to catch out workers not adhering to policy before the authorities do) and you can fail on any of the conditions of your license and face concequences even if, once again for those who are hard of thinking no laws actually have to be broken, or even potentially broken.
Some places I've worked failing a test purchase is a disciplinary offence.
You can be as annoyed as you like, complain as much as you like, be superior and condescending towards the staff all day long - it will not change. And really, it's hardly the end of the world, in the grand scheme of things if you don't get a bottle of booze, it really isn't that big of a deal, and the reactions to it happening are ridiculously over the top and precious - like when people start talking about power and jobsworths 🤣 grow up, you're really not that important and there's no big conspiracy to keep people from their precious booze.