@MAGICDAVESHROOM
Here's a converse thought - with absolutely nothing to back it up. But who knows?
What if those costumes actually had a detrimental effect during Battlez? What if the small amounts of time taken while redrawing those extra few pixels that make up the costumes actually slowed down the game for the player?
With one plant it would make hardly any difference, but what about when you have 20, 30, or 40? Especially those that, like the Dusk Lobber as an example, move a lot during its lobbing cycle.)
The game mechanics are geared around the stock plants, but who's to say that each plant with their appearances altered doesn't take a few micro-seconds longer to cycle through their various animation sequences?
Like I said - just a thought.