Because HTC is a MUCH better (i.e. more competent) company than Motorola. They (HTC) also care a lot about their end-users unlike Moto.
I'm not trying to be argumentative or bash on a company but this statement is far from the truth.
HTC is notorious for shipping out sub par cheap hardware (radio, touchscreens)
I'm not speaking about one device. I'm speaking in general. They make a new device every other day you would think they would get it right or at least flip for better hardware.
I don't call that caring about their end-users. One of the biggest reasons I jumped ship on RIM beside's Android was poor build quality and skimping on QA. I will not support companies that practice business like this.
Motorola builds a lot of their phones to Mil-Spec so they know what they are doing and you cannot deny that the Droid is one of the best, if not the best, built smartphone on the Market.
Again I don't want to make this into a war of phones.