Honestly mostly because I'm lazy. For a while it seemed like RR was just in a constant flux and I didn't feel like dealing with issues. Yours has just worked. Thank you for your work.
You don't need to permanently unlock the bootloader. You just unlock it long enough to install twrp. Once you have twrp you can flash whatever you want.
I'm using att. On the Jan 11th build I use the nextgenphone APN and volte works perfectly. Newest build I don't get the option for enhanced 4g LTE mode. Mcc 310 Mnc 410.