Nobody other than Apple gets to sell unlocked through carriers. The last iPhone we bought I purchased through Apple just to ensure that it was factory unlocked. This allows my son to flip between AT&T or Verizon.
Main Android flagships with AT&T or Verizon have been pushing their updates through carrier first and releasing to unlocked devices about same time. OEMs do this because in USA, they always have and will consider the carriers as their customer. I purchased AT&T PRIV wholesale although I'm on AT&T. It's carrier locked. I had the infamous "No Service" issue.
Although it was brand new in the box when I purchased the PRIV, AT&T would not help me out with the issue. Fortunately, the problem was fairly large and many small business accounts had the same problem. AT&T, with BlackBerry, fixed the problem using software update pushed out to devices. Later, I purchased DTEK hardware from ShopBlackBerry and put the factory unlocked devices on my AT&T lines.
Those devices have screen quality issues and I don't have the carrier leverage as I normally would. The updates really haven't been much better factory unlocked compared to carrier locked. BB in later years outsourced it's logistics to Digital River. BBMo infrastructure at this point is worse than BB ever was. BBMo infrastructure should get better however, AT&T software and hardware support is more valuable right now than any perceived factory unlocked hardware advantages.