It’s slowly happening - a great many small electronics have been transitioning to various USB connectors for charging (everything from bicycle lights to small drones). Those are all 5V though, which is great for typical one cell lithium, which is 3.7-4.2V, and where 500ma-2A is the most you’d need or want anyway.

The issue so far is that for higher power levels or voltages the electronics are still complex and expensive, even with the PD standards, so it adds a lot of cost doing it that way compared to a typical barrel connector.

Maybe in another 4-5 years and with some standardized and hopefully dirt cheap PD chips?