Well, there is a difference between Machado’s image being bad and not being as good as Harper’s.
In fact, I re-looked at the marketability article and it was from 2016. Harper trailed only Kris Bryant, but that was also right after the Cubs won the World Series. He’s probably more marketable than Bryant right now.
Machado does seem to be disliked by fans and Jesus Aguilar, but is he really so unpopular teams are avoiding him? It’s not like the other marquee free agents are falling into big deals left and right. Dallas Keuchel, for example, is still out there despite having a Cy Young award and no negative stigma whatsoever.
Most likely the reason is simple Occam’s Razor - Machado wants more than anyone wants to pay and no one thinks he is as valuable as his agent does...