Once people decide to buy something, usually they want compliments on / validation for their choices. It's ironically unpleasant for people to be told "no, don't waste your money!" Especially because he probably spent some good time coming up with that build, being told "no, waste of money" was the correct and helpful advice, but (if he even read it) might have been upsetting.
One's ego very often gets wrapped up in decisions made, not necessarily for any good reason.
Oh well, we write for the 9/10 that are just reading and not commenting, not necessarily the actual interlocutors.