I'm going to (for the sake of discussion) ignore how pricing benefits on an a la carte level is something that the networks are not designed to do. Let's say a lawsuit forces Visa and Mastercard to allow this and to convey a tailored product cost in interchange to the merchant to present to the cardholder for surcharge consent and the slow moving payments industry rapidly updates their point of sale integration to facilitate this.

Individually purchasing these benefits would erode their value to the point where nobody would use them.

When you use a benefit like extended warranty, or purchase protection, or rental car damage coverage, at the end of the day, these are insurance benefits. Amex is a rare case of self insurance (these benefits are administered by Amex Assurance Company). When you don't, you contract them from another benefits company. Citi loves Virginia Surety. Many smaller financial institutions and some larger will just use on Visa Card Benefit Services, which is Asurion. Even things like Priority Pass or other lounge access are essentially. You're not paying list.

These are benefits which your issuer and the benefit provider have calculated the value of and accordingly priced. Not everyone with an Amex Platinum is going to go to a lounge twice a week. Not everyone with a Chase Sapphire Preferred is going to make an rental car damage claim. So you spread the premium or cost of the benefit among your entire cardholder base that you're offering the benefit to. The benefit is priced accordingly for the issuer. Obviously someone with an Amex Plat card is more likely to make a trip interruption/delay claim, but I know people who could have and never did.

If you get to the point of making the benefits separable to the point where there's a discrete fee on each purchase, then you're going to end up with self-selection that makes the benefits untenable to offer. 10 basis points extra that I get surcharged for extended warranty? Okay, I'd take that on an Amex that I essentially only use on electronics purchases. But then I'm much more likely to A) have opted into the benefit because I'll use it B) only use it for purchases in which I need said extended warranty coverage. That reduces the amount of overall swipe fees amex gets, reduces the charges to ones I'm potentially going to make claims on, and I've self selected to pay for that benefit because I'm going to use it. This factors into premiums for the issuer; if use of a benefit goes up, they're going to pay more for the claims and the cost to adjust them. Do I rent a car once a year or less or do I do it weekly? If I'm on the road 75-100% of the time and work doesn't cover LDW I'm probably gonna buy that. But if not, I'm probably going to buy LDW from the rental car company or risk having to claim damage on personal auto insurance.

This is ostensibly why Citi killed Price Rewind (Price protection). Services like Earny would automate a price protection claim for you. For me, with my time, I would have to notice a price difference of at least $25 to say a claim is worth it, and I'm not omniscient of every sale on the planet, so I would only look for larger purchases. Earny would automate sending price protection claims by scanning your inbox and submitting them to your issuer for any amount in exchange for a 25-30% tithe. All of the sudden you have claims going in front of a human being for toothpaste being a nickel less. Citi's premiums for this are predicated based on the cost to directly pay claims, and the cost to administer them. Earny decimated price protection pretty much everywhere (stragglers exist) by stuffing the claims inbox with claims that were way more effort in administrative effort (people work and earn money for a living) than their claim amounts, to the point where Earny became an affiliate cashback site like Rakuten or Honey.

Similarly, if you made it so Amex Platinum was self selecting and you could do a checkbox on different benefits, they wouldn't be priced the same either. If Centurion lounge access was separable from the entire AF, you'd have a lot of people opt out. Or people in NYC where there's no Walmart to get grocery delivery from opting out of that. Or people outside major cities where there's no Equinox gyms opting out of that.

Again I'm rambling, but a la carte benefits on card charges are not going to work. Part of what makes the benefits cheap is that most benefits are insurance policies subsidized by people who rarely or never claim. Which is not that different from health insurance in the US at large employers, where large health plans have cheaper premiums than individually purchased ones.