First of all, Toyota's drivers weren't the best F1 had to deliver, but they were pretty decent drivers. They pretty much did what the car ought to have been doing throughout the years.
Secondly, McLarne has a chance, yes, to win the constructors championship, but the odds are stacked against them. The leading team has the best car, and apart from a few odd poor results from Webber, Mark will always bring home whatever points Vettel left behind. Plus, they are quite far behind anyway, chances are they won't be able to out score Red Bull at any other race this season.
Secondly, regarding sponsors, they'd much rather see a team just run along for the rest of the season, to come back and become race winners and championship contenders next. You have to think long term, what will serve them better over the long term? Focus 100% on this almost wrapped up championship, lose this one, then be a step behind next year, lose that one as well, then what are you going to do? How about, nevermind this one, come back and win the title next year, and become the team to beat? Sounds good to me.