Why might members of parliament follow party discipline under closed-list elections?

In the context of neoinstitutionalism, members of parliament follow party discipline under closed-list elections primarily because the institutional structure of the electoral system grants party leadership significant control over the political future of individual candidates.

Under a party-list system, seats are awarded to candidates based on the order in which they appear on a list compiled by the party. Because the party leadership determines this ranking, a candidate’s ability to secure or retain a seat is often contingent upon maintaining the favor of the party’s inner circle. Consequently, party discipline acts as a mechanism to ensure that representatives adhere to the party line, which serves as a guarantee to voters regarding how a candidate will perform in office.

Furthermore, in systems where the government’s survival depends on maintaining a legislative majority, party unity becomes a matter of institutional necessity. A single adverse vote can trigger the dissolution of the legislature, compelling members to maintain a united front to ensure the government's stability and their own continued political influence.