No. of Recommendations: 5
Republican Tim Miller wrote an article that was published this morning, "They Served With Trump and Saw the Crazy. They Should Endorse Harris," that asks why the individuals who worked for and alongside Trump did not appear at the DNC to speak out against him or to endorse Harris.
There's also option #5 - they think it's better for the country if a Republican wins the Presidency, no matter what the personal flaws of the Republican.
Most of the folks who served in the Trump administration are going to be a die-hard Republicans, for the most part. They're going to genuinely believe in the Republican mission statement, and generally don't want Democrats to be able to implement their policies.
My personal choice would be #6: none of them would have been welcome on the terms that they would be willing to participate in. In order to participate, folks like Mitt Romney or Mike Pence (or the other actual high-ranking folks that Tim Miller mentioned) are going to want to be able to write their own speech and have final edit over their copy. They're going to want the same freedom to do what Sean O'Brien - to go in and tell the Democrats that they're wrong on a bunch of policy matters, to the point where the crowd is gasping and on the verge of booing. I'm sure that Mike Pence thinks Donald Trump is dangerously unfit to be President, but he's not going to stand on a DNC stage and say it unless he can also make it clear that he thinks Harris' positions are terrible on all the other things he cares about. That he's not trying to elevate the Democratic Party generally (which I think most of the other GOP speakers ended up doing), but that he's just pointing out how singularly terrible Trump is.
I doubt the DNC would have ever invited Mike Pence in a million years, and they wouldn't have invited any of the other ones on Miller's list without final edit over their speech.