A lot of different theories were offered regarding this phenomenon, many of which were interesting in their examination and the changes within society that act as catalysts for such movements. Social media played a big role in the discussion, which makes sense in this age of instant gratification and demand to share your opinions. Other factors included the national broadcast vs. the local broadcast, color commentators who played for certain polarizing teams, and simple psychology and jealousy.
One interesting point that was made was the advent of technology that allows fans to choose their broadcast team in most circumstances, especially with local broadcasts (since national broadcasts usually don't provide multiple options due to their exclusivity). If you purchase the MLB.tv package, for example, you are given every audio and video feed of every game all season so long as you are not blacked out. So if you're not a fan of the home broadcast team on television, you can always switch over to the visiting radio feed while you go run some errands. Sometimes, having this choice gets fans to shut up because they don't have to listen to announcers they detest; other times, it fuels their fire even more by simple contrast.
Whatever the reason people may have to hate announcers, the biggest question that I raise is: who cares about your opinion? Why do people feel the reason make sure everyone knows their disdain for someone behind the microphone? And why do they feel the need to make sure the announcers know it as well? That would be like if random people came to your job and complained about how you do it. Eventually, you'd go crazy.
Look, there are even announcers for which I don't care. But I don't take the time to send a Tweet to those people to let them know they're terrible. If you can't escape what you deem to be awful announcing, just hit mute! Why spread the hate?