Reactive form array not adding object to form group with attribute

Question

I am working on Angular project, in this form is generated using reactive form.

For now initially I am adding one field by default on the form. This is the code to add the data :

 this.objectFields.push(this._formBuilder.group({
        fieldLabel: [{ value: 'name', disabled: true }, Validators.required],
        fieldType: [{value: 'text', disabled: true}, Validators.required],
        fieldName: [{ value: 'name', disabled: true }],
        dataSet: [],
        required: [{ value: true, disabled: true }],
        displayInGrid: [{ value: true, disabled: true }]
      }));

As initially the method to insert data is called it only adding :

dataSet: null

Remaining fields are not getting added to the form group.

If I add this as :

 this.objectFields.push(this._formBuilder.group({
            fieldLabel: ['name', Validators.required],
            fieldType: ['text',  Validators.required],
            fieldName: ['name'],
            dataSet: [],
            required: [true],
            displayInGrid: [true]
          }));

The HTML code

<div fxLayout="column" fxLayoutGap="5px" fxFlex="35%" class="detail-form-column">
                                    <mat-form-field appearance="outline">
                                        <mat-label>Field Type</mat-label>
                                        <mat-select formControlName="fieldType" required>
                                            <!-- <mat-option value="">Select</mat-option> -->
                                            <mat-option value="short-text">Short Text</mat-option>
                                            <mat-option value="long-text">Long Text</mat-option>
                                            <mat-option value="extended-text">Extended Text</mat-option>
                                            <mat-option value="date">Date</mat-option>
                                                                                            <mat-option value="number">Number</mat-option>
                                            <mat-option value="checkbox">Checkbox</mat-option>
                                            

i.e. without object of value and disabled attribute, then its working fine.

Why the form group not adding the object with value and disabled object?