There's already precedent that having a state medical marijuana card already makes one ineligible, and using as an ID when trying to purchase a firearm is grounds for automatic denial by the seller. Hawaii, which requires all firearms to be registered, went even further, proactively cross-referencing their gun registry with the medical marijuana one (https://www.leafly.com/news/politics/surrender-your-guns-pol...).
It's not really surprising that the law is so broad, given that it was written in 1968 when anti-drug craze was still ramping up. The reason why it doesn't get amended is, I think, because it manages to touch two third rails at once: Republicans don't want to be perceived as "soft on drugs" by their base, while Democrats are afraid of being seeing as not sufficiently aggressive wrt "gun violence". And so, here we are.