Because they are designed to prevent users from modifying or installing new software on their devices, locked bootloaders are a touchy topic in the Android world. They are a big pain for ROM developers, and as such, there has been a recent push for manufacturers and carriers to ship devices with unlocked bootloaders that allow users more access to their devices.
The movement has been successful in getting manufacturers like HTC to offer bootloader unlock tools, but another bit of the effort was an FCC complaint directed at Verizon for having devices with locked bootloaders on their network. The basis of this claim is that the block C licensed spectrum that many devices run on is supposed to be free of locks, and therefore Verizon should not be able to lock bootloaders. Far from swaying them, though, the complaint only prompted a formal response letter, which includes the following:
"Verizon Wireless has established a standard of excellence in customer experience with our branded devices…Depending on the device, an open boot loader could prevent Verizon Wireless from providing the same level of customer experience and support."
As far as I can tell, this letter is trying to say that Verizon Wireless cannot offer unlocked bootloaders because they would cause problems for customer support. While theoretically this could be a true concern, realistically it shouldn't really be much of a problem. The kinds of users who unlock their devices and install custom software shouldn't be the type to expect Verizon's customer service to fix their problem.
Unfortunately, there will always be a few ROM users who get a friend to unlock their device or buy a modified phone on eBay and then try to call customer support. It is quite annoying that these few people have to ruin it for the rest of us, but there's not much we can really do about it. Verizon is dealing with this the way any business would, even if it isn't best for the device modders out there.
So, while it's not great that Verizon has decided to lock bootloaders due to some users, that is probably just something we will have to get used to. Users still have a choice though, and if you don't like the policy, then you can either switch devices, carriers, or even deal with the frustration of unlocking the bootloader yourself.[Droid-Life]