some comments on the follow up posts. Typical windshields are 2.0 mm glass, 2 pieces, with a 0.7mm thick vinyl layer in the middle, giving a 4.7 mm thick windshield. This is pretty thin. 2.3 mm glass is actually cheaper than 2.0 mm glass because it is easier to make and you scrap less from breakage (higher yield). Or at least it was cheaper 12 yrs ago when I worked in glass. So, aftermarket windshields are typically not thinner than OE. The OE mfg doesn't use as much 2.3 mm glass because it is heavier, and takes longer to defrost. But, we did get Subaru to change to a 2.3 + 2.0 glass windshield to save them some $. You use the 2.3 mm glass on the outside for obvious reasons.
Windshield tooling, used in bending the glass, is very expensive and, in general, is not sold off over time. It can be used indefinitely but does require "maintenance" like everything else.
OE glass can switch suppliers, but it is not like every month Toyota puts a different brand windshield in a camry. The reason is they contract a company to make the glass and then the company, and or, Toyota will buy the tooling. Again, the tooling is expensive. And, in general, you are contracted to build the glass over the life of the vehicle. When I worked glass we were the sole supplier for every windshield we made. We could not sell our glass to the aftermarket because of our agreement. This is fairly typical for other auto parts also as the mfg often owns the tooling the part is produced on so they can control the output and insure they get it and it doesn't go to the aftermarket. The aftermarket can produce glass but they must develop their own tooling. So, they buy a few windshields and put them on a CMM and measure, and then reverse engineer the tooling.