I see where you're at, and have seen many folks suggest the same of this design. Counterpoint - our rivers, lakes, and waterways have a long and proud history predating iron and coal (especially when considering their significance to pre-colonial native tribes like the Lenape, Susquehannock, Erie, and others) and will have a much longer history outlasting those industries. That shade of blue was also altered from the COA to match the US flag, representing PA's pivotal role in national history (taking the role of the Eagle in our COA).

(Full disclosure, I'm the one who put this design together 5yrs ago! Glad to see it's still sparking good conversation. 🥰)