The cost of license is completely arbitrary. To ilustrate, regular price of L4 license is $45, but at the same time hAP mini, complete hardware with L4 license included, is $19.95. So what's the cost of license there? It's more like free bonus. It's the most extreme example, but it's clear that even with SXTs and other not too expensive devices, the cost of license is not $45.
But more importantly, look at it from customer perspective. You buy the whole package, functioning device. If it breaks and it happens soon, there's warranty and you can get replacement from seller. But if it breaks later, but still too soon, meaning that as customer you really expect the thing to survive longer than warranty is (it's usually not very long), then what?
If it's something like infamous RB4xx capacitors, you can spend a little bit of money, time and some curse words directed at MikroTik's quality control, but in the end you have functioning device again and you can be happy. But if the problem is with another component, you repair it, the hardware is perfectly fine, but you're stopped by software, it's doesn't feel good. Even if it's not MikroTik's fault like capacitors were, perhaps something just burned because of power spike, it still sucks.
MikroTik has no obligation to give out replacement licenses for user-repaired devices, it would just be nice thing to do, make the company look more friendly. It could be worth few lost sales of new devices, it can't be that much.
People who quote full posts should be spanked with ethernet cable. Some exceptions for multi-topic threads may apply. Not intended as incentive for masochists.