The mentality in keeping the name CLINTON front and center was to remind everyone that Clinton was impeached, a chain adulterer, thief from white house.. and she enabled him.
Somehow using Hillary, distances her from that name.
I guess it is a small nuance but I have seen it several times and might be valid
Too many people are still nostalgic for Bill. that is why I think “Rodham Clinton” is the bestter approach