Can someone tell me why Michelin withdrew from F1?
Do you think F1 has 'lost something' having just one tyre manufacturer?
Michelin's decision was based on the FIA mandating a single control tire requirement. Michelin was in F1 for competition and was not interested in being a single tire provider. It was rather lopsided though as most of the teams were Michelin leaving the rest to use Ferrari spec'ed tires. The result was Ferrari always being first among the Bridgestone runners.
A side effect of this FIA regulation is that several drivers are having to unlearn Michelin wear, operating window, grip & braking characteristics that is adversely affecting their performance. This is a big deal as the drivers in this category include Kimi,Alonso, Button, etc. and may account for their relative lack of speed in the first 1/4 of the WC vs their teamates. Knowing the rubber is big when it comes to a driver's commitment into a corner on the limit!

'For many people life is something that flits by while you are busy doing something else.' Alan Henry 06/07 F1-racing - The Rumble Script.
Or as I like to say 'life eats up a lot of bandwidth!'