Why?
Irreversible transactions are not desired by anyone in payment networks. Consumers don't want to get scammed out of money. Merchants want customers to feel like transactions are low risk so they are more willing to make them. That's a big reason why merchants put up with the outright hostile to them system of chargebacks. Sure, you will lose some money to chargebacks you might think were not valid, but you have made much more than that back from liberalized spending habits.
Nobody benefits from irreversible transactions except fraudsters and other bad actors. And they benefit soooo much from transactions being irreversible. Why would you build and advocate for a system that explicitly empowers bad actors over anyone else?
An escrow is not a solution. The escrow itself could be a bad actor.
I've intentionally used irreversible crypto payments to a merchant that is an an industry with high chargebacks. It is highly useful in transactions where the merchant is highly trusted but the buyers tend to be weasels. Such merchants tend to charge high premiums for reversible payment methods.
In such cases it is win-win for both the merchant and customer, the customer doesn't have to foot the reversibility overhead and the merchant is able to offer goods at the same profit margins but lower price which should yield more sales.
The existence of wire transfers, cashier's checks, and, you know, CASH undermine your claim that people in payment networks don't desire irreversible transactions.
Basically everybody who's ever sold something in person wants to know they get to keep the money when the other person walks away with their stuff. It's the fraudsters in those everyday transactions who want reversibility.
I am much more likely to buy something if I can pay with a credit card. Making a wire transfer is stressful; I'm worried that I got the wire instructions wrong, and my money will go to the wrong place and be gone forever. Paying with a cashier's check is stressful; I worry that I will get mugged between the bank and wherever I'm spending it, or that I'll just lose it on the way. Cash isn't quite as bad, and I almost always have some cash on me.
But given the choice of paying with cash or credit card, I will almost always choose the credit card. I like the idea that if I walk away from that transaction and then later realize that the merchant sold me something defective or outright fraudulent, I will have some recourse in getting that money back.
I get that a merchant will prefer an irreversible transaction, all else being equal. But I don't think all else is equal; I absolutely buy the GP's argument that purchasers will be more liberal with their spending if they don't have to worry so much about the merchant being a scammer. And regardless, there are many many more purchasers than merchants, and most (if not all) purchasers would at least have a slight preference toward a reversible transaction.