Firstly, I didn't blame HTC, I blamed Verizon, hence "So where the OEM's allowed flexibility, the carriers swooped in to fill that void."
Secondly, throwing the issue of "blame" aside and trying to imply that the planned obsolescence phone is somehow the fault of the consumer, you need to consider that until very recently, you had to buy a specific hardware variant of the phone if you wanted your phone to work on Sprint or Verizon, because of the CDMA networks. It wasn't a matter of being a "Verizon-branded" phone. If you wanted to use the phone on Verizon at all, you had to buy the Verizon-specific version (even through HTC directly), and if so, the bootloader was locked.
Not everyone has the luxury of being able to switch carriers if your current carrier is an ass, because they might be the only one servicing your area. So if you're on Verizon and you want a smartphone, there was a time when that meant you were likely bootloader-locked.