I don't think they mention maintenance burden specifically. Using a framework with packages means you have to track upgrades, do upgrades, check release notes, breaking changes, support and end of life cycles, license changes, etc. It's a have maintenance burden if you keep it live, even if you don't intend to make any changes.

Vanilla doesn't have this problem. Server-side has it too, but in a slightly different flavor.

The heavier and integrated the framework, and the more additional packages you include, the heavier the burden.