Because it will be a condition for the peace treaty with Syria just as the Sainai was for peace with Egypt. Assad would be murdered immediately otherwise.
If it isn’t already a done deal, and Netanyhu is elected, I don’t see him giving up the Golan. I think that’s why Ohlmert was so despised; he was seen as giving strategic parts of Israel away to her enemies, in the hope that by doing so, they’d say they’d leave Israel alone and he could say that there was peace. There’s no peace, if there’s no security.