This, of course, ignores the simple fact that they do not, actually, need new forms to make and sell new toys. Old forms sell new toys too! As someone who buys a non-zero amount of merch and who knows people who buy a lot of merch, the well for making new merch based on older content and material does not seem to be close to drying up any time soon. I could be wrong about this, but I can't imagine there's ever been that much internal corporate demand to give Goku a new form if, say, "Super Saiyan 1 Goku" merch is selling just fine; and since there's seemingly always merch of Super Saiyan 1 Goku, I am inclined to assume it sells well enough for it to continue being trotted out. They also (thankfully) keep making new Tao Pai Pai merch, so I can only assume he sells well enough that they haven't felt the need to give him a new form to sell toys of.
Now, naturally, having a new transformation does add to the list of things they can make merch of, but.....so does everything else as well! New characters, new outfits for existing characters, new designs for existing characters, new vehicles, new MacGuffins. Any new story is a rich opportunity for merch generation, transformations or not. In Daima's case, we have Glorio, Panzy, Goku (Mini), Vegeta (Mini), Piccolo (Mini), Bulma (Mini), and more. In Super's case, we had Beerus, Whis, Shisami, Jaco, Zeno, Zamasu, Gowasu, the Gammas, and more alongside new outfits for Bulma, Videl, Goku, Vegeta, Trunks, Goten, Pan, and more. Take the sentence "they made this new form so they could sell more toys" and replace "this new form" with "Goku (Mini)" or "Vegeta's RoF armor" and it's probably just as true, but more transparent in its (lack of) intellectual content. New stuff sure does exist to make money.
To be clear, I'm not saying not to voice criticisms of new transformations in general. But "oh this design is bad, obviously they just wanted some new merch" is not only lazy and thoughtless, it's also not even necessarily accurate. For all we know, the powers that be genuinely thought they were cooking when they wrote and designed [that one new form that you, the reader, REALLY hate].
Suffice to say, I think "they needed to sell new toys" is less than a nothing criticism regarding new forms. But let's pretend that it was a good and serious angle of critique for just a moment and ask the question: does it even work as a money-making strategy? How well does it work? Do action figures and other forms of merchandise for freshly debuted transformations outsell those of older forms, or characters without transformations? Or is it a bad financial strategy, because new forms don't actually sell like crazy (or at least not to any unique extent)? And if it's a bad financial strategy, how much sense would it make to continue assuming said strategy as the impetus for any given new form's existence (and only the new form, apart from new stories, outfits, designs, characters, techniques, etc.)?
These are genuine questions and/or food for thought. I do not have any relevant sales figures, and I wouldn't know where to find them, but I would like to if anybody has them and/or knows where to look. Partly because this is such a cliche talking point that it deserves to either be definitively vindicated as a valid truism, or tossed in the bin so that discourse can improve just that little bit. I know Baggie_Saiyan was pretty knowledgeable about the various merch that's been announced and released, but I don't know if he was also knowledgeable about their sales figures (he also seems to be on hiatus from keeping up with this stuff anyway).