Index creation using 1 core only

I've been working on an environment where every index creation is happening on a single core. Big or small indexes/tables. Even when I force MAXDOP in the creation it still ignores it and runs on a single core. * MAXDOP is set to 0. * Available cores are 24. * Cost threshold is set at 5. * The index creation cost more than 1000. * SQL configured memory is: 160GB, even though 128GB is max. SQL Server running:

-none
Microsoft SQL Server 2019 (RTM-CU18) (KB5017593) - 15.0.4261.1 (X64) 
    Sep 12 2022 15:07:06 
    Copyright (C) 2019 Microsoft Corporation
    Standard Edition (64-bit) on Windows Server 2019 Standard 
        10.0  (Build 17763: ) (Hypervisor)

Why is it not able to go parallel?