May I propose a contrarian narrative?
I see experienced founders use the "stealth mode" veil specifically because they are focusing on execution and don't really want to waste time in polite conversation debating the merits of an idea or rehashing a list of competitors. Talking too much about ideas is deleterious to the focus needed for building products. Sometimes the brain needs a break and a person wants to connect with other human beings for something other than work.
I'm sorry you weren't able to judge the last 5 people based on their ideas! You found another way, bravo!