Why is anything modular a good solution over a USB-C DAC-containing dongle cable?

Modular ports are a physical disconnect between "thing that routinely experiences stresses and has a relatively short expected lifespan under heavy use" and "extremely expensive and long-lived motherboard", usually a separate circuit board connected by a ribbon cable. They serve a completely different purpose from a dongle that converts a common port to a less common one.

Framework laptops have another decent strategy, where you've got on-motherboard ports that have relatively few usage cycles, and are protected from most forces because the easily-replaceable custom-dongle-squares are held in place quite securely. They take the damage, protecting the motherboard. And as long as the motherboard ports are still good, you can even forego the modular thing and just plug in directly if needed.