The most humble meters come free in a kit, since you're really buying the test strips, and they all have onboard memory and an optional app.

It's extremely unlikely the owners of those meters would even be able to use any other app. There's no standard for the device data sent over bluetooth to the app. There's no USB port. Beyond 90 days of data (many meters have 99), A1C is preferred. Reverse engineering to support alternative apps is also unlikely since there are always new devices to hack.

SugarTrack, and other apps like it, sit in a weird deadzone. The most likely users either have a nicer meter that already does offline export, or they have a crappy meter but prefer the official app or tracking their stats on paper anyway (in their food journal). Again, the app is always optional unless it's from a super sketchy brand that isn't even cheaper.

There's no room left for doing weird somewhat low-tech things in principle anymore. The market has moved on. The most common layperson user wants integration across all their health apps. The most common nerd user buys the nerd device. The manufacturers have known this for at least a decade.