[nhumrich]

If they knew the answer, the headline wouldn't be a question, it would be a statement.

[js2]

The headline is ambiguous. It could be inferred that the question is answered in the article.

A clearer headline would be: "Scientists are trying to understand why the coronavirus spreads so easily between people."

[ksk]

Well, to be fair, its not meant to be a textbook or a journal article where being super explicit matters much more. It's a fun article for laypeople like us.