Bottas has switched to world champion Mercedes for 2017 following the shock retirement of Nico Rosberg, with Williams releasing him from his contract.
However, when Ferrari showed interest in the Finn in 2015, Williams was less cooperative, and that situation played a part in the outcome this time around.
"Valtteri has been an important part of Williams, he's got that fiery passion ... Keep reading

Source: Williams "promised" Bottas release to top F1 team