US drug control agency will move to reclassify marijuana

"One major effect of this is that weed stores will be able to use banks and payment processors legally once the regulators catch up."

Assuming banks/processors don't decide to restrict them for other reasons.

Wouldn't that be leaving money on the table? The bank that accepts business with marijuana vendors is at a competitive advantage to one that doesn't, no?

Not necessarily. It depends on the risks, morals, and stuff like ESG. We've seen this with stuff like alcohol, tobacco, and guns.

But you can buy alcohol, tobacco and guns with just about any payment method?

Porn and gambling are probably better examples. They're kryptonite to payment processors due to the chargeback risk.

There is no liquor store in the country where you can't pay with a card. Well, maybe not Uncle Ted's Moonshine Shack, but realistically it's not something anyone has to worry about. Different funds may not invest invest in those thing, payment processors might charge some businesses a slightly higher premium, but Visa/MC are not gonna police your legal consumer purchases.

Gambling is actually illegal trough, no? AFAIK porn is the only proper example

Gambling varies by type and jursidiction.