That is true. That is why attackers (like the NSA) would be happy to infiltrate routers (less changes from the outside like administrators) instead of clients (more changes). A proxy is a quality target, too. But a proxy is also more visible and tampering is usually easier/faster to detect. Corporations need to TLS and/or message encrypt everything. But that is often not priced into (project) budgets and a hard thing to do (key exchange, managing certificates).