With GM just about bankrupt and looking for billions of bailout money in the US and EU then its no real surprise they had to pull out.
And as Gow has said the series has actually grown all the time over the last 6 years with less and less manufacturers, which is true. So I guess it shows that people dont really care if a team has works support as long as the cars are there and the racing is good.
http://www.btcc.net/html/generalnews_detail.php?id=1381