Distributions continuously patch packages. It's necessary to be able to ship a working, integrated distribution at all. It's also necessary because users expect some level of consistency and integration between components, and distributions are the spaces where that can be achieved. Usually these achievements then get upstreamed so it's easy to forget about their origin. There's also the cases where distribution users just fundamentally disagree with upstream policy and use their ability to change Free Software to make it happen - such as the disabling of auto-updates in distribution packages coming outside the distribution packaging system, or the disabling of [opt-out] telemetry.

So there are many good reasons distributions patch. It's not reasonable to paint them all with the same brush. If you want to credibly criticize this, you need to be more specific.