Why go to a restaurant and ask "can I get a diet Coke, please"? Why not admit that you'd consider other sugar free, carbonated, cola flavored soft drinks?
Because both parties should already be aware that it's a negotiation between people and not a blockchain contract to be mechanically evaluated according to a spec.
Indeed, you say "can I get a Coke please", not "it must be a diet Coke" - or if you do, you probably want to make it clear that you'd not consider alternatives. Similarly, enough companies use actual-must in job offerings (for all or for some requirements), and enough companies are clear about (some) requirements being a preference that expecting candidates to divine which employers do and which don't mean it when they say "must" means you'll loose out on some candidates, for no good reason.
So that it weeds out rational, reasonable, honest people and the company can continue to receive people who are prone to overconfidence, lying, and other pro-social psychopathic traits.
