Database field is not created when publishing customization

Acumatica 2021R2

MySQL 8.0(tested on 5.7 as well)

When publishing this code, it publishes successfully but the database field doesn’t get created. What am I doing wrong?

using PX.Data.ReferentialIntegrity.Attributes;
using PX.Data;
using PX.Objects.AM.Attributes;
using PX.Objects.AM;
using PX.Objects.IN;
using PX.Objects;
using System.Collections.Generic;
using System;
using PX.Objects.EP;
using PX.Data.BQL;
using PX.Objects.CS;

namespace PX.Objects.AM
{
  public class AMWCExt : PXCacheExtension<AMWC>
    {
        //only enable this class if manufacturing is enabled
        public static bool IsActive() { return PXAccess.FeatureInstalled<FeaturesSet.manufacturing>(); }

        //WorkcenterEmployee field
        #region UsrWorkcenterEmployee
        //the acumatica database type is PXDBInt
        [PXDBInt()]

        //set the UI display name
        [PXUIField(DisplayName = "Employee ID")]

        //set the default value
        [PXDefault(PersistingCheck = PXPersistingCheck.Nothing)]

        //the ui control type is a selector
        [PXSelector(typeof(Search<EPEmployee.bAccountID>),
                                    typeof(EPEmployee.acctCD),
                                    typeof(EPEmployee.acctName),
                                    SubstituteKey = typeof(EPEmployee.acctCD))]
        
        //define the field
        public int? UsrWorkcenterEmployee { get; set; }
        public abstract class usrWorkcenterEmployee : BqlInt.Field<usrWorkcenterEmployee> { }
    #endregion

    }
}