Not everyone does. Of those who do, some simply disagree with his political views - now, this doesn't require that you hate someone, but there is a significant portion on the left who count their own political stand to be based on their keen insight, caring for others, and the boldness to part with tradition . . . this means that when others think different ideas might actually solve our problems more effectively, the left count them to be stupid, uncaring, and lacking the boldness to part with tradition. Again, not all on the left, but those who imagine that their political position is the only viable stand if you're smart and kind and courageous - which, again, means they think those who see things differently (like Limbaugh) must necessarily be stupid and mean and fearful.
Others perceive him as arrogant. Limbaugh presents his views from a performed persona that is arrogant and unyielding . . . for decades Liberalism has entrenched itself as the elite viewpoint of the elite crowd - sitcoms regularly mock conservative views, all the coolest people (actors, musicians, etc) are liberals, and the youth (since the 60s our barometer of cool) are naturally inclined toward a liberal take on things . . . Limbaugh's approach is that conservatives stop apologizing for their conservatism, that they don't publicly defer to the popularly promoted liberalism, that they don't adopt the left's scenario that conservatives are stupid and mean and fearful. So he adopts the opposite disposition and defiantly asserts his own intellect and rightness, etc - and many liberals don't 'get' it and believe that he is actually that absurdly arrogant (which, of course, is all part of his 'evil' scheme).