Renault and Toyota to quit F1 together?

i wonder why every time some team is about to quit f1 someone thinks and says that toyota will quit as well....why???they must be thinking it because toyota has not delivered as a team what they expected...i remind you that toyota chose the hard way (chassis & engine) and not the easy one like the germans...(only engines).and even with the easy way the germans (bmw) are already gone in order to focus to environmentally friendly cars...something that toyota is doing 12 years now!!!so leave toyota alone...and take into consideration before speaking its motorsport involvement and the results of that!!7 titles in wrc.just 2 years in le mans 2nd position because of a flat tyre...nascar..etc