down in the article, basically the 2 well known key things - socialization and a "well tired dog is a well behaved dog" - got broken as an effect of the pandemic lockdowns:

"The phenomenon of behavioural problems in dogs who missed out on socialisation and training opportunities during lockdowns has been well documented, too.

Added to this, Lloyd says, the return to hybrid or full-time, on-site work now means that “a lot of those dogs are spending more time in isolation and they’re not used to that. The doorbell goes and it’s the most exciting thing that’s happened to them all day. They’re increasingly territorial when they protect the home.”"

Also it sounds like a UK specific thing - postal deliveries deep into private frontyards. In US the postal boxes are on the edge of the property.