A continuous grant is a different thing than a momentary one
Background location access permits an application to continue receiving a device's location while the application isn't actively open or in use, rather than only while someone is directly interacting with it. This is a meaningfully broader grant than access limited to active use: it means the application can track movement continuously over time, building a pattern of where someone goes and when, rather than only ever seeing a location snapshot at the specific moments someone happened to open the app.
The two grants answer genuinely different questions — 'may this app see where I am right now, while I'm using it' versus 'may this app track everywhere I go, indefinitely, whether I'm using it or not' — and conflating them into one bundled 'allow location' prompt hides a decision most people would actually want to make separately if they understood the two were different at all.
Why the distinction deserves its own explicit prompt
Presenting background access as its own separate, clearly labeled choice — distinct from ordinary in-use location access, and ideally requested only when the app's actual functionality genuinely requires it — respects that a person willing to grant one may reasonably decline the other. An interface that bundles the two together, or requests background access upfront regardless of whether the app's core function actually needs it, is asking for more than most users would knowingly agree to if the choice were made genuinely clear.