Because

1. Physical dongle tends to break, and when it does, they expect us to give them replacing parts

2. They do expect bug fixes-- especially calculation bug fixes-- as the bugs are discovered. It's hard to leave their production critical apps broken like that once you know that the bugs can cause monetary or even life loss.

Wanting to say in business makes sense, bug fixes make sense.

But the actual dongle... look, something like that should have a 30+ year warranty. There should be a plan for how to replace it a couple times before making the initial sale.