a lot of sellers, both auction and otherwise, just want to make the money and really don't care about a lot else.
For instance, when I was among the biggest sellers of original comic art & illustration, someone sent me a pin-up pastel without disclosing that the piece was heavily scratched. Fixing pastels is nearly an impossible job, but the dealer had me bring the piece to their restorer who really looked down at this type of art and commented "well it's only illustration, what's the big deal"
so in his mind, if it wasn't what we call an 'easel painting' to him it's low art & doesn't deserve the same respect.
I'm sure Ewbanks and others have this same attitude and when you consider that the majority of items they otherwise sell via their auction are of higher values, while the movie posters go from a few hundred to a few thousand, it doesn't engender their interest as heavily. It's wrong, but this is where the buyer or seller makes their decisions on who to deal with, when the time comes.
for my part, my collections will be sold by Heritage and Profiles in History. Both companies that know what they are doing and will get the best prices, two issues of paramount import.