Syria knows that if Israel and the Palestinians reach an agreement that passes a referendum in the West Bank, then its negotiating leverage against Israel will dry up. It will be hosting a discredited and marginalized Hamas leadership. It can extract the best terms from Israel as negotiations progress (if they do). If an agreement is reached with the PA, and Hamas leaders can be expelled from Syria at the same time, then Israel will be willing to pay a high price.
10 arrested at Israeli Arab protest in Ramle (Haaretz)
from the article: U.S. confirms intense efforts to restart Israel-Syria peace efforts