Why did Tryndamere, Zyra, Lulu and Varus (And maybe Draaaaaaaven too?) not get a Texture rebalance? I mean, Tryndamere could use more than that anyways (And look like he does in his splash/icons/huge statue), and while Zyra, Lulu and Varus don't look THAT bad, they could use some polishing.

The TRs were meant to hit the worst of offenders, giving a larger increase due to the delta between what was there and the work required. That was something we needed to do due to the sheer volume (I believe our final stat was like 300 champions/skins total).
We have a LOT of content in this game. The problem with that is our quality bar increases faster than we can ship and address things that are behind. As an example, League has 126 or so champions. Zyra was only 25 champions ago. So the TR Project was something that we found time to do during our normal work schedule to try to boost that bottom line up. That's why we didn't go for some of the more recent characters, even if they could be considered for it.
But, to your points...
Draven: Could use it, just to simplify some of the shapes and business on his texture. However, people might perceive this more as a sidegrade rather than something wholly positive.
Lulu: I think she's pretty good. Needs a new model (yordle unification pass where) moreso.
Varus: Not bad, but a little soft. His contrast is good, and he follows the visual hierarchy already.
Zyra: An interesting case, as we actually have someone doing her in her free time. HOWEVER. Zyra probably has the most amount of textures per skin, due to all her plants. Additionally, there was a fun problem of how plant like her skin should be versus human, etc. etc. In short though, too high of scope for a simple project.