Might have something to do with keeping the opco's completely separate to comply with the RLA but who knows?
Your .com app actually does do it, so it doesn't seem to be a RLA thing. .com will show all services/cost and transit days. When you get into your larger customer software Fedex does not have their core systems doing such a thing, now you can get Fedex to custom program that in if it's a deal breaker for you. But if the goal was to get Ground in over Express, why wouldn't their higher volume software just assist customers, hold their hand to save them money and make Fedex more?