I think this actually had to with the specific legal framework some of those banks were chartered under. "National banks" were established under a specific cha

I think this actually had to with the specific legal framework some of those banks were chartered under. "National banks" were established under a specific charter type, which included the authority to issue paper currency under certain Federally-sanctioned conditions, so a lot of them took names that focused on them being National Banks. Thus, you got a lot of First National Bank of Pacoima, Second National of Pacoima, Merchants National, Totally Not A Scam National, etc. Even though that ended in the 1930s, the precedent for a lot of "First" and "National" names has persisted.