Actually those are good marketing reasons. Otaku buy DVDs more than mainstream in Japan. Sheryl is too old for the demographics for this title and if they weren't interested in the female demographic then Alto would have been drawn and motivated differently.
Sheryl may be 17 yo but her actions and mannerisms place her at age 25 and above which is good for what she does for a living but not so good for a female anime protagonist since there is an age limitation apparently. See R1 Witchblade volume 2 booklet page 3.
True Tears may be paying for its misstep
already but we won't know for sure until the subsequent Oricon data comes out.