Rather than making even more costumes for Last Round, they should have just included all the old DLC in the game. The characters also only got
one new outfit (that wasn't DLC before) for DOA5 Ultimate, not several. To be honest, I think the characters have more than enough outfits already, especially the girls. DOA has basically become a fashion simulation at this point. And it's no wonder, that we see so few real graphical updates for the current generation versions of Last Round, when all the graphic designers are stuck making more and more costumes, hairstyles...and tweaking the boob physics.
I'm 95% sure that the graphics updates you want are being saved for DOA6.

from a business standpoint, I wouldn't improve the game too much so that when the next one is revealed, even the minor graphical tweaks will seemingly make it look better when compared to its previous game. CoD does this shit all the time. (Still waiting for a rainy stage)
Also, for DLC, I would rather have the good sets, rather than all of them. If they could just not include the disappointing ones in the free batch, that'd be great. But I was damn surprised that they didn't have the 2013 Halloween outfits and the other DOA5/+ bikinis.
It would only make sense to add these missing packs:
5U School Uniforms
5U Gym Class
Ultimate Sexy Swimsuits
Halloween 2013
Nurses
Bath Towels (should've been free to begin with)
Marie Rose debut costumes
Phase 4 Debut Costumes
Nyotengu Debut Costume s
My guess is, that if they added all of the DLCs, there will be a flood of "Omg TN, I bought all of the DLC, and this is how you REPAY ME?" people. Also, TN obviously didn't add all DLCs so that they could still make money whilst in preparation for LR, because some people are still buying the ones that weren't included, so they can have all costumes.
And if people are going to compare the USFIV argument, Let's just say this:
AE: Characters got 3 alternates.
DOA5/U: Characters like Lei Fang and Ayane get at least 30-35 extra costumes. And they are giving out 180 of them for free.
TN just can't give all of that for free. They can give out at least half of that, but not all. Why? Koei might not be letting them, because they still want to make the bread before it expires.