The primary, perhaps sole reason to be a Trump lackey is to be in a cushy position (and keep it) when he croaks. That's also known as the Vance Dance.
But many of the dumber stooges fall victim to Trump's demands that they go all kissy kissy and slander Trump's "enemies." The repercussions of that far outlast a lackey's term of Turd Service.
Giuliani was particularly stupid in this respect. Trump didn't even give him a pat on the head, and threw him under the bus almost immediately.
No honor among thieves.