The original article actually says:
one can find in canonical texts—in particular, the Vinaya or monastic discipline—another notion of consent, one based more on inner affective states than verbal permission. As a clear standard for ethical sex, this Buddhist consent falls short of the affirmative consent upheld by many institutions today, but it also challenges our contemporary approach to sexual ethics in healthy ways. Indeed, each idea of consent reveals the other’s strengths and shortcomings.
Which I think most can agree to. So, the author’s title seems a bit like click-bait (she acknowledges that the Buddha did teach consent in the Vinaya), but her real point, which I think is accurate, is that the Buddha is never recorded as specifically recommending only proceeding with sexual acts after receiving verbal affirmation that those acts are welcome.
As for why we have no records of him ever saying that, or more broadly giving any sort of sutta on the detailed ethics of consent for laypersons, I think there’s two categories of explanation: explanations of why he wouldn’t have touched on the topic, and explanations of why any such suttas wouldn’t have survived to the present day.
So far as I am aware, the Buddha never gives any advice on how to have sex at all. He describes sex (such as when confirming that sex between a mother and father is a necessary cause for human life), and advises against it, but that’s it. It’s possible that nobody ever thought it was an appropriate question to ask.
It is also possible that at one point he did advise laypeople on how to have consensual sex free of misconduct, and that sutta was irrelevant to the monastics, and probably also not terribly well received by the laymen. If the buddha had said, “only proceed with sexual acts after receiving verbal affirmation that those acts are welcome” who would have memorized it and passed it down? It’s conceivable that a layperson did ask the Buddha for this sort of advice, and then promptly ignored it and continued to engage in marital rape with his multiple wives.
What is clear however is that his reason for not addressing this was not approval of marital rape or any other form of rape not already covered by the five precepts. Because such a teaching (approving of non-consensual sex) is not in line with his other teachings (most crucially - he does not approve of those who mortify others).