You're leaving out the most important bit of a component like InlineStack: the props [0]. Yes you can just apply `display: flex` to the div you're working on, but like any proper abstraction these guardrails make using flexbox correctly the easiest path forward (the "pit of a success").
[0]: https://github.com/Shopify/polaris/blob/eb6161f6b4e02679b5e8...