Yes, the main reason why it has happened is the strategic value of Crimea (Donbas was not so lucky in this regard...), but the overwhelming local support (which

Yes, the main reason why it has happened is the strategic value of Crimea (Donbas was not so lucky in this regard...), but the overwhelming local support (which originated from factors like ethnicity, culture, language, poor Ukrainian rule, etc.) made everything much easier and cheaper for Russia. I highly doubt that with a hypothetical level of support 50% or lower Russia would have risked to take such action.