Can't set admin defaultColumns for collections

I'm assuming that the admin defaultColumns are the columns displayed in the admin ui for its given collection.

If I add 'clientName' to the defaultColumn array and set useAsTitle: 'clientName', nothing seems to happen

const CaseStudies: CollectionConfig = {
    slug: 'case-studies',
    admin: {
        defaultColumns: ['clientName', 'author', 'category', 'status'],
        useAsTitle: 'clientName',
    },
    access: {
        read: () => true,
    },
    fields: [
        {
            name: 'clientName',
            type: 'text'
        },
        {
            name: 'clientWebsite',
            type: 'text'
        },

My admin UI only displays the author, category and status column as can be seen in the screenshot. No clientName.

What am I doing wrong?