You might think it's defeatist, but it's realistic.
The shop owner can ask them to stop and get a mouthful of abuse as well, and what do you do when they say no? When they say they're not leaving? Physically remove them? Put yourself at risk of being hurt and also of prosecution yourself for laying hands on someone?
And don't say phone the police because they don't have the time to deal with more serious crimes due to lack of resources, or things like shop lifting and even if they do attend, it's not very likely there'll be many, if any concequences.
I've watched a couple of episodes of a police programme recently where assaults on officers are 'punished' with fines of £150-200, if not dropped all together, so if the justice system doesn't take assaults on police officers seriously, who most people are concerned about the concequences of crossing, why is abuse of a shop worker going to be any different?
This is a societal problem and it shows in places where society gathers like shops and pubs, it's really unfair to place the policing and prevention of that behaviour on people who aren't employed to do that, and are also some of the least respected in society, and then blame them for being ineffective.
They may be representing the business, but it's also not the job of the business to police people's behaviour, their business is selling goods in return for money, not making sure people behave themselves appropriately in public. They employ staff to facilitate that business, they also have to now employ more staff and training and equipment to deal with the behaviour - at extra cost which is passed on to the consumer.
Someone mentioned up thread that shop staff are being trained in conflict resolution, and a fair few places now have body cams on their staff - are they spending that money because of a defeatist attitude or because they're recognising that there's an issue and because they have a duty of care towards their staff, they are taking steps to address it?
The issue is lack of concequences for this type of behaviour, and worse right through society.
And having been the subject of a social media witch hunt that named and shamed me (mistaken identity as it happens, I wasn't even on shift at the time) on local social media, it's not just about a Google review of Sainsbury's not getting ready by many people, it can be absolutely devastating for the person on the recieving end.
It's not about shops or their staff 'allowing' anything, it's about not being able to prevent or stop it because there aren't the, back up, tools or resources to do so.
People need to stop placing the onus and responsibility on stopping and preventing this behaviour on the people it's directed at and start placing the onus on the people doing it.