Ødegaard knew he wasn't gonna be starting for them but signed anyway, that's my point. He could've signed for a team with a shorter way to the first team, but he didn't. He could've gone to Ajax which would've been a great move for him. He could've gone to Liverpool where there's a manager who's not afraid to use youngsters, and it's even his favorite team. But ultimately he signed for Real Madrid, like I said probably because they had the biggest wallet. And besides, Sterling is easily Europe's best 20 year old, both Bayern and Real would definitely give him plenty of chances.
As for the whole "wanna win trophies", that's what every player wants. But if he wants to win European trophies like CL, he's obviously better off at Bayern or Real than City or Chelsea. If he wants to win PL, his best bet would be to stay at Liverpool for the time being. And not because we're gonna win it "next season", but because we all know Mourinho doesn't stay in one place too long, and City have an aging squad and are gonna have to deal with FFP sooner or later. Moving to one of those clubs now could easily prove to be a bad decision in a couple years time. He has plenty of years ahead of him, his career has barely started.
He says he wants to be as good as he can be, and where better to continue his development than the club that made his breakthrough? That gave him the chance as a teenager, are playing him week in week out, and are offering him enough money to buy a house every month?
As for your question "How can you be certain he will?", I've already stated I'm not certain at ALL that he'll sign a new contract. If you go back just 1 page, you'll see that I'm only 50% certain - it could go either way. But to me it's obvious why he hasn't signed: Money. His whole interview was him repeating he's not a money-grabber, but he even admitted that he'd have signed a year ago for much less money. To me it sounds like he's pushing for money, and if that includes a move away, then he'll move. If Liverpool accept his demands (which they probably won't) thEen he'll stay.
If he does go to City or Chelsea, it's gonna be a new British transfer record, that's for sure. As for the Webster ruling, I can't see that happening even in a parallel universe.