The tooling gap exists partly because git's data model has no native concept of "this branch's upstream is another feature branch" — each PR is independent from the forge's perspective, so rebasing one layer in the stack requires manually re-targeting every PR below it. FAANG-internal tools solve this by storing the stack relationship in a metadata layer outside git itself, then regenerating the PR graph after each rebase. Without that layer, the bookkeeping falls on the developer, which is why most teams abandon the workflow after two or three levels deep regardless of how disciplined they are.