A few things:
First of all, they're always spouting lore about a thing (a concrete object or specific idea) not just "Tribes and Towers."
Then, the GM asks "so how do you know about <the thing you're spouting lore on>?" That narrows it down quite a bit. Does the thief really know about arcane creatures from the deepest depths?
Then, even if they trigger the move, they're always taking a risk. If they get that 6- result, something goes wrong. The GM gets to make a move. Is it really worth that risk?
Lastely, standing around and thinking for too long is likely a golden opportunity to the GM to make trouble. You can't just stand around a dungeon thinking and assume nobody will notice.