Conservative comedy has been terrible for a very long time. Fox News tried to compete with Comedy Central (really) by releasing their own 'Daily Show' called The Half-Hour News Hour. I watched one episode and it was painfully unfunny. For example, this was when Obama was a rising star and they did a bit that lasted at least five minutes about how bad Obama smells because his initials are B.O.
Even back then before I knew who Obama really was, I thought, "isn't this like a joke from a radio show from the 40s? Who uses the term 'B.O.' anymore?"
There have been some very funny right-wing comedians. The ones already mentioned are good examples. Another is P.J. O'Rourke, who wrote some hilariously funny books, in part because he had no problem attacking his side as much as attacking the left.
That may be the biggest problem with conservative comedians today- they only attack the left. They don't hold a mirror up to themselves. Some of the best comedy is self-reflection and they aren't capable of self-reflection.