It's a very visible thing when people do it. It's not common where I'm from, but if 1,000 other people go to a store, then just one person leaving a cart in an awkward place pisses off 999 others.
It doesn't take much to make it seem like a lot of people are being inconsiderate, when it's much more likely that a small minority of people have a very wide reaching emotional impact.
You mean the USPS that can send a letter to anyone in the US, no matter how remote, for less than $1.
The USPS that has had its funding messed with for decades by Republicans trying to make private shipping the only option?
The USPS that is guaranteed by the Constitution to exist and provide services?
...
Yeah, let's ditch this amazing service that provides stable union jobs everywhere in the US, and just let private industry take over, that works so well every other time we've done it.