What is causing these water heater pipes to rust/corrode?
Looks like minor leaks, compounded by mixing galvanized pipe and copper/bronze valve without using dielectric couplings between dissimilar metals.
Honestly, any plumber installing NEW galvanized pipes (rather than just making repairs to existing) in the past 5 years is doubtful. If you really want threaded pipe, stainless is available and lead-free, which galvanized iron pipe is not.