I don’t agree with the given answer to “Why the PO wants you to estimate”. The author cites external reasons (made commitments etc) that shouldn’t have been there in the first place.
Sure, in some lines of software development you really have a “deadline”, if you are working towards some event or launch date. But most of the time estimates are needed to determine *if it is worth it*. Can it be built in 2 weeks, let’s go. Is it gonna cost 2 months, then let’s prioritise something else. That isn’t to say you always have to go with the shortest te build features (you can apply "CD3" – Cost of Delay Divided by Duration), but you need it to compare alternatives.