Most are in fact. When I searched for "USB C cable" on Amazon just now, I had to scroll to the 16th result to find a non-USB2 C-to-C cable.
When I search for "USB C cable" on Amazon UK, 90% of the results are A-to-C cables. The first C-to-C cable is an Amazon Basics 2.0 cable, so you are right.
Absolutely. They're often used as charging cables, e.g. on cell phones and Apple laptops, where engineering a high-speed data cable of the length required would be costly, difficult, and unnecessary.
Apple calls them charging cables. The advantage is they are less expensive for longer lengths.
They're less expensive, they're more flexible, and if you want to go to 3 meters long you don't have to worry about signal integrity.
Yes and since they are very thin they are quite useful when you just want to carry a tiny charger (my choice is the Mu One / RAVPower GaN 45W same Navitas charger except the Mu One has nifty folding international heads) and a lightweight cable. AmazonBasics is a reliable brand for this.
If they aren't, they will be, once the value engineering kicks into full gear :)