Some do. A lot of companies that use Duo will set that up for their internals. The problem is that those push solutions require that the company have some mean

Some do. A lot of companies that use Duo will set that up for their internals. The problem is that those push solutions require that the company have some means of communicating with the app that you're using to trigger the push and the confirmation (as far as I can tell). This technology works around that by letting the browser talk to the plugged in device, circumventing all of the network/api bits.