Everything used to be less slick. Even huge store chains and brands look amateurish by modern standards, from as recently as the 90s. Some of it's explainable by changing fashion making those things look worse, but most of it's just that less was designed, and expectations for how (say) a Wal-Mart's exterior (and interior, for that matter) would look didn't include the whole building being "on brand", to pick one example.

I think graphic design becoming much faster and cheaper, and elaborate custom-designed and custom-printed/manufactured signage, wraps, et c., becoming far cheaper to make, is part of the cause.

I also suspect much of this is a very visible case of Graeber's "Bullshit Jobs", specifically of the "zero-sum competition" variety—which makes sense, given the relation of this to marketing and ad-spending. I don't think Target having the entire facade of its buildings designed & built to be "on brand" does very much good of any kind, per se, nor do brand-driven price tag or end-cap sign designs and such, and the (apparently) increasing tendency to tear down rather than repurpose—I assume because making the old building fit your design system would cost about as much as building new, anyway, and if you build new you also get... a new building—sure seems socially harmful. However, they feel they have to, so they don't look shabby next to all their competitors.