We be offered a candidate we can all respect?

Two reasons:

1) Jeh Johnson didn't choose to run for President; and
2) If he did run for President and became the nominee, you'd certainly stop respecting him.

The first is pretty inarguable. The second might not seem like it would be the case, but any Democrat who actually had a chance to get the nomination would immediately be subject to tons of Republican and conservative oppo attacks. The same is true of any Republican and Democratic negative attacks, BTW. So non-candidates often seem like they might appeal to a broad base of both parties - "candidates we can all respect" - because it's advantageous for the opposition parties to make the non-candidates look better than the actual candidates. Which usually means highlighting the one or two policy areas on which they might disagree with their parties and come closer to the opposition party.

Most relevant example in the current race - if you think that Nikki Haley seems "reasonable" to Democrats now, just wait and see if she actually won the nomination. Then she'd be portrayed as the most horrendous person imaginable.

Anyone progressive enough to actually have a shot of winning a Democratic primary would immediately be savaged by the conservative/Republican groups once they reached a point of success in the polls. The same would certainly be true of Johnson - a few months of savaging him as a tax and spend, pro-choice, pro-gay rights (he spearheaded the effort to get rid of DADT), climate-change believing hippie, and all the folks who now respect him because he says critical things about Democratic border policy will turn on him faster than you can say "John McCain."