Well, they kind of promoted the match without really "promoting" the match, if you know what I mean. Many assumed that Austin and Rock would obviously end up in the finals, and that one of them would be the undisputed champion. So a lot of people bought the PPV thinking going in that Austin and Rock were fighting, only to end up surprised when the match was made impossible the moment Jericho defeated The Rock.
They've done this sort of trickery before - the tournament brackets of Wrestlemania 4 were set up so that if Randy Savage and Ricky Steamboat won their first matches, they would square off against each other in the next match. And this excited many people, as they thought they'd get another classic Savage/Steamboat encounter out of it, which people had wanted to see since their classic match at WM3 a year before... but it didn't happen. Savage won but Steamboat didn't. They pulled the same stunt at King Of The Ring 1998, having Ken Shamrock and Dan Severn (who had fought in the UFC before) in the semi finals of the tournament to make it look like if they both won, they'd meet in the finals but they didn't (Severn lost.) Not that anyone would have cared at all about a real-life UFC rivalry carrying over into a fixed wrestling match but the logic is still the same.
For the record though, the long term plan was Austin staying heel and keeping the title until Wrestlemania X-8, where the titles were supposed to be unified when he lost to The Rock (who would be getting his big revenge there for what Austin did to him the year before.) But obviously, several factors caused them to change plans on that one (Austin not wanting to stay heel, Hogan coming in, Rock already having one foot in Hollywood and already planning to likely leave again after WM18, which he did.) They even shot a publicity photo in October of 2001 where WM18 was supposed to be (in Canada) with the mayor of Ontario pretending to pull them apart: