My take (straight married female): eye/ear candy, AND good/relatable person. Bonus points for the sense of humor.
Another plus for me is that he got in such good shape doing actual, honest, productive work, not just from the gym.
I don’t, but I’m an ophidiophobe.
I think my favorite was when he delivered a calf. A good deal of kindness to the cow, very cute moment with the calf (“Welcome to the world, Chief!”), another nice moment with the cow (“Nice job, honey”). What’s not to like? 
Yeah, there was another episode with farm animals. They were inseminating horses, and took us thru the entire process. It included “harvesting” from the male, whose member was blurred-out so as to not offend our Victorian sensibilities. Then, Mike got to put on a full plastic sleeve for the insemination part (with female horse’s tender bits blurred-out). The lady he was with was very non-chalant about what was going on “well, that’s it - we just created a baby horse!”.
I don’t think this segment was aired more than once.
I can’t remember who it was, but one couple on the Dope had as their “arrangement” that he was allowed to sleep with Kari Byron if ever he got the chance, and she was likewise allowed to sleep with Mike Rowe. So yeah, I’m aware that many female viewers have a crush on him.
I don’t, but I can easily see how someone inclined that way might. He’s got a friendly personality, he does good, honest work, and insofar as I can judge such things, he’s rather handsome.
Also ear candy. He does have a very nice voice, both speaking and singing (he originally tried a career as an opera singer).
NOOOOOOOOO!
On the other hand, I suppose that increases the odds that I will be able to knock back a male heterosexual beer or three with him sometime.
Right, it’s not just looks, but his truly amazing ability to flirt with anyone. As a straight man, to me it’s more like watching an outstanding athlete, enjoying the point where he manages to punch through the defenses of some crusty 58-year old seen-it-all cleaning fish guts, and get her to smile and giggle.
In fact, that’s the show I really want to see. “Mike Rowe flirts with the unflirtable”. Obviously they couldn’t admit the point of the show up front, so they’'d have to be pretending to do another “Dirty Jobs” type show, but the main point is putting Mike in the room with the dourest, least flirtacious women imaginable and seeing how long it takes him to get a smile.