The doorbell should have a straight mounting box in addition to the wedge to allow room for the installation wiring as described in the instructions.
The wedge mount is fine for some locations, but others really need a straight mount.
Most doorbell buttons only have a tiny hole in the wall for the wiring. The provided flat mounting plate does not provide anywhere for the (provided) wire nuts and additional wire to go, and enlarging the hole in the wall may be impossible (brick/cement) or inadvisable (renters or people intending to remove the wyze doorbell in the future).
Adding an additional mounting box would add very little to the production cost and would remove lots of frustration.