Why did many Syriza members oppose the 2015 bailout agreement?

Many members of Syriza opposed the 2015 bailout agreement because it required the implementation of austerity measures that directly contradicted the party’s core platform.12

Syriza had risen to power in January 2015 on a mandate to end the severe debt crisis policies—such as cuts to pensions, labor rule changes, and tax hikes—that had been mandated by the "troika" (the EU, IMF, and ECB) during previous administrations. When Prime Minister Alexis Tsipras was forced to accept a new, draconian bailout package in July 2015 to prevent financial collapse and a potential "Grexit" from the euro zone, many within his party viewed the deal as a betrayal of their anti-austerity commitments.1345

The opposition was significant: 32 Syriza members voted against the initial agreement in July, and nearly one-third of the party refused to support the final version in August. This internal revolt ultimately led to the resignation of several deputies, who went on to form a new party called Popular Unity.1