When Quickshare drops your Wi-Fi connection, its not Direct anymore, that's just soft AP from an error, and if that doesn't work, it fallback to Bluetooth. Bluetooth is used for provisioning as well.

The only reason why many apps don't use it is because of buggy implementation, some phones require a full restart after using Wi-Fi Direct to fix connectivity issues, even Motorola's own product line with Smart Connect use it only with certain models, despite having Wi-Fi direct due to poor implementation (can be forced). They even have a white list of supported adapter for the Windows app since direct is used as well, can be unofficially force enabled for Mediatek based adapters (rare on some laptops).

Back in 2016 things were much stable on Android phones with Wi-Fi Direct, even with old Blackberry, there were many apps including file managers that used it before it was essentially dropped, even for onboarding/provisioning apps like HP printers...

Apple's Airdrop success is about gaining traction, in the era of Wi-Fi Direct or other methods, most people were not aware of such features, as it required an app to be installed, they used email/messaging, even when Airdrop was first introduced and preinstalled, it took years for the average person to use it.