They do, at least in India, even to this day. You pay ₹500 for Ubuntu, and around ₹7k for Windows 10 Home and ₹12k for the Pro edition. You can also go for the no-OS option, which costs ₹0.
I am pretty sure it can be flashed, similar to how we do it for RISC-based boards. For the sake of convenience, they make easy money out of the customer.