I can't believe this needs to be said but it's not supposed to get 60,000 people to Wembley.
It's supposed to replace the trains effected by the maintainance works.
An 11 carriage Avanti train carries 500 people. The buses are going to move 5,000 people. So 10 full trains. Lime Street to Euston is hourly, so fans would probably be on the 7, 8, 9, 10, 11 oclock trains, any later than that and you're not making kick-off. Piccadilly to Euston is more common but 5 full trains worth of people from the FA plus the 2400 fans the club have organised transport for should get most down there.
They aren't supposed to be replacing travel for every fan who would driven, gotten a train from elsewhere in the country, gotten a bus which would have run anyway.