There is one very good reason: the discharge curve. An alcaline battery loses voltage when it discharges, the lithium ones discharge with the max voltage until they suddenly stop working.
This is a reason insulin pumps require specifically high quality alkaline and lithium is considered a risk.
Lithium primary cells have a shallower discharge curve than alkaline, but not completely flat; measuring state-of-charge is essentially trivial for any competent design engineer. Medtronic specifically recommend FR6 lithium cells in their insulin pumps.
While the Medtronic pump has a setting to toggle between "Alkaline" and "Lithium" to adjust how it reads the battery percentage, the Dana i is primarily calibrated for Alkaline (LR03).
This is a reason insulin pumps require specifically high quality alkaline and lithium is considered a risk.