For very large brands, composable can sometimes be a necessity.
If you have a very complex infrastructure and need to reconcile and integrate tens of different systems, composable allows you to clearly identify the System of Record (SOR) for certain data points, map the integration paths between all your systems, and give you more granularity and control over how different systems talk to each other.
With that said, brands tend to overestimate their need for a composable build. Sometimes, you just need to spend enough time simplifying your infrastructure (a good thing in itself), and the need for composable goes away.