The stated reason they didn’t want to make DLC characters for BL3 is because supposedly people just stuck with whatever character they first picked. The DLC characters (Gaige and Krieg) apparently weren’t popular enough or played enough to warrant making more characters for BL3… and then they only get the two DLC characters from BL2 to be primary characters of the DLC for BL3.
EDIT: @Bremen1 also pointed out that the DLC characters from TPS were also major players in both the first DLC and the main storyline of BL3. Good catch.
IDK. I just get a very bittersweet chuckle out of that.