Centralized OS application transparency limit vs dapp

Hello! I'm new to this world, but i used to be a web developer. I searched a lot, i asked to chatgpt, but it gives me partially correct answers. So, the question is, if we can already develope open source applications getting GNU GPL license ( garanting the highest open source ), what's the point of developings dapp based on Blockchain, if we can get the same transparency with centralized os applications? I get the " server thing ", it's great to avoid using a database present only in one place, managed by only one entity, is it the only reason? Could you give me an example about the " transparency limit " blockchain overstep over GPL licensed os applications?