For example, anecdotally, the percentage of founders I've heard say that they only want to hire early-20s engineers, is... high.
(PG might've started it, with influential essays about why he wanted college students as founders, perhaps making it socially acceptable. Then people like Zuckerberg reinforced it, with public comments. Many companies structure their interviews around tests/rituals that arguably start from "How, uh, fresh in mind are your undergrad CS classes, even though that probably has little-to-no relevance to the actual work you'd be doing here?")
That's only ageism. There's also sexism, racism, classism, genderism(?), etc.
There's enough of those biases going around, and we're in/hitting a recession. Not everyone can afford to decide "I don't want to work for a company where anyone who could influence my opportunities has some ill-informed bias against some group.".
Some scientific finding of X is fine, if the science is solid. But being aware of ongoing bias problems can affect how we communicate and think around that.