First, not using DANE doesn't mean using MTA-STS. In particular, between the giant mail hosts, even if both sides publish MTA-STS information and validate MTA-STS elsewhere — I'm quite willing to bet they have a bunch of policy overrides for each other. In a way, MTA-STS is nothing other than standardizing those policy overrides so things don't break as much when they have to change something.
Second, in terms of installations, DANE absolutely wins, just because there are a few giant installations and a ton of small ones. Even if the quota on the small ones is bad, it'll still outweigh the giants by orders of magnitude. And it's technically far easier to roll out a new mechanism on a handful of giant, well-automated, well-monitored installations. They could all do DANE in a few weeks or months. They just don't want to operationally/politically. Conversely, updating millions of small shoestring installations to MTA-STS (or something else) is a herculean task.
(Related question: what about domains? That's yet another statistical perspective, considering a lot of domains point at Gmail & co.)
And lastly — I'm not sure your statement is in fact correct, because the medium-sized enterprise senders sending in bulk generally don't use the actual e-mail giant infrastructure (e.g. Outlook.com, Gmail.com), even if they're hosted at a corporate cousin (Azure, GCP). And that's probably enough volume to shift the outcome for "most Internet mail". For this, it'd be interesting to know what the various cloud-ish mail solutions (aaS & products) do, which I unfortunately don't.