A block from Mojang for one server's EULA violation does not stay contained to that one server — it lands on the shared IP address, which every other tenant on that same node happens to be reachable through too.
Why the block reaches further than the server that caused it
Mojang's blacklisting operates at the IP level, not per-account or per-server. On shared infrastructure, several tenants' servers are reachable through the same public IP with different ports — a block on that IP for one server's pay-to-win violation makes every other server behind it unreachable to any client checking against that list, regardless of whether those other servers did anything wrong at all.
The account responsible for triggering a shared-IP blacklist is liable for the disruption it causes every other tenant sharing that address, not only for the consequences to its own server — this is a direct, foreseeable result of how IP-level blocking works, not an unusually strict policy.
Pay-to-win perks affecting gameplay balance are the core violation category — cosmetic-only purchases (skins, particle effects, non-gameplay ranks) are the standard safe path for servers that want to monetise without risking a block.