The biggest aspect is that now there are so few "human" interactions with organisations because so much is done online, there are far fewer staff. In the old days when literally everything was in person, there'd be a small army of real people whether in shops, office front desks, banks, utility firm town centre offices, town centre tax offices, etc etc. They'd be dealing all day with the "routine" stuff that was straight forward and simple, so the "odd" complaint or awkward customer was diluted by the dozens of "normal" nice customers with no problems. They'd also have a hierarchy of a mix of younger inexperienced staff and older more experienced ones, so the young would learn by watching and emulating the ones who'd been there longer, and the young would be able to pass on "problem" customers to their colleagues literally next to them.
Now so much is done online and remotely, the few customer service staff are now dealing predominantly with problems/complains as all the customers with simple issues/wants can be dealt with remotely/automatically online. That means the few real people left on the front line are dealing constantly with problems and complaints and are generally low skilled, not much experience, etc., so it's no wonder they're jaded with constant problems and customers are suffering with poor customer service due to lack of experience and "fed up" staff.
It's noteworthy that a few excellent organisations have far higher skilled and experienced staff on their front line, people who are more likely to deal with customer problems properly to the customer's satisfaction, who have the experience to know how to fix problems, and yes, experience in how to handle to difficult customers.
Personally, I'd never buy so much as a power lead from Currys or Argos because my experience of their staff is appalling going back years/decades, as their front line staff (counter and call centre) generally havn't a clue about consumer rights re faulty products, legitimate return rights, etc - to the extent that some of them look at you like you want them to sacrifice their first born child when all you want is to get a refund for a laptop in accordance with consumer rights laws! Contrast that with the likes of Amazon and John Lewis, where returns are hassle free, whether for change of mind or for faulty items.