Speaking as a lifelong DW despiser, I know why I and thoudands of others can't stand him.
It goes back to his driving days. He was brash, obnoxious, pushy, and irritatting. Those were his good qualities. No doubt about his talent...he was a good driver. But his personality and his moth earned him the nickname "Jaws". He was a brat and a whiner. He once wrecked another driver's car on the cooldown lap after the race. It was that driver's only car, and it just so happened to be his only career win. Jaws kept a man named Lennie Pond from taking his car to victory lane after his only career win because he wrecked it after the race was over. Real nice guy.
He spent the entire decade of the 1980's whining and crying. He is the primary reason we have something called restrictor plates at two of our tracks. He stated that he was tired of following "that red Thunderbird", meaning Bill Elliott, a man who dominated speedways before restrictor plates. Waltrip's incessant whining, non-stop crying, and ceaseless belly-aching are among the big reasons our sport was introduced to the single most dangerous change ever made to a stock car, all so he could keep up with a Ford.
Plus, if you ever get the chance to hear him, you'll know why people dislike him. He's a buffoon. He'll comment for ten laps about how loose a certain is on the track, then the pit reporter will interview the crew chief of that car who will say that the car is so tight the driver can't control it. This happens at least once every five races.
There are those who like Jaws. I know not why, I'm sure they can tell you Lord knows I couldn't. I've seen people say he's funny, or interesting, or adds something to the broadcast. That's fine. Make up your own mind. Just please know that he is far from representative of that era of drivers. Most of those guys had brains and common sense, despite Jaws' total lack of both.