Toyota following Honda and BMW exiting Formula 1 - no success despite all the money spent

It's really kind of a pattern. Big car manufacturers want to expand their image of building sporty cars. They enter the Formula 1, throw big money at it and are fairly unsuccessful. With the overall business not doing well they decide to pull back and exit the racing series. We have seen this with Honda, then with BMW and now Toyota!
There are many questions you could ask, for example, would they have canceled their racing engagement if they had been really successful? And, why haven't they been successful, given all the money they invested? Let's take Toyota. They were known as having the biggest budget of all the teams, they had it all under control, the chassis, the aerodynamics, the engine, everything. And still, besides some memorable results, the expected success didn't come.
On the other side you have Brawn GP who inherited the developments and ideas of the Honda team and won, despite a smaller budget and initially a lack of sponsors, the formula 1 championship. A private team showed the established factory teams how to do it.
Is it really about individuals that make the success? Designers like Adrian Newey, team leaders like Ross Brawn, drivers like Sebastian Vettel and maybe Jenson Button? It seems to be like this. With with all the big teams walking away the Formula seems to become again what it once was, a series for semi-private teams competing with what they were able to build.