Finally someone actually mentioning the code. In PoS "trust" must exist along several points in time before you can engage with the system - and the most notable point being trusting that the rules (written in the code) are of your desire.

With PoW you don't care about the software code. The rules are dominated by the PoW because it literally proves to you which is the chain where most people are interested in, because literally no single entity could burn that much electricity.

With PoS on the other hand you kind of need these checkpoints in the actual software and then you have to activate this entire new trust model where you have to trust the client code, and where it came from etc. I could literally come up with an entire fake chain on my computer and present it to you and without client-checkpoints there would be no way for you to not accept my chain compared to your current one.

With PoW I don't have to trust anything. If the majority next year decides to change the rules, so be it. The majority has spoken.