Because it’s a trustless system. In order to override the system you have to take over 50% of the nodes, and in large enough systems it’s infeasible to get that much compute power. This means that no one person or organization can actually control the destiny of the system, only the consensus can.
I can’t believe that here, in the fediverse of all places, we need to have a discussion about the benefits of having a system that corporations can’t control.