This graphs says it all. Incredibly low marketing spend relative to sales. How do they do this? Its called retention marketing. They manage to acquire and keep customers and remarket to those customers so effectively that they are able to grow the customer lifetime revenue on each customer.
On average, I spend less than 5% of my revenue on retention marketing versus 10-35% (depending on the channel and campaign) to acquire new customers. It is far cheaper to retain customers than to have to constantly be acquiring new ones.
To do this, focus on selling direct to consumer to capture their contact information and remarket to them to retain them and grow customer lifetime value.
While small consumer startups may not yet be able to afford the AI capabilities of Stitchfix, deploying a database to capture customer information and transaction data is dirt cheap and easy to do, which is what I have done.