Actually, some of the action cameras are producing 4x the detail, not sure about Gopro since the Hero 6 seems to have a few issues, but the Yi 4K+ does have 4x the detail of a dashcam with 1080 sensor, except where it is more motion blurred because the sensor is not so sensitive.
Some of the latest 4K small sensors are now sensitive enough for dashcam use, maybe similar sensitivity to an IMX233, maybe next years will match an IMX 291 with the same size sensor, and then there will be no reason for not using them in dashcams other than price. Currently the biggest issue is that none of the dashcam processors can write a high enough bitrate to store the 4K detail, but that should change soon. If you want 4x the detail then you need 4x the bitrate, so around 100Mb/s. The Amberella A12 can't do that, and Novatek cant do it currently, the cameras that can are $300+, too much for a dashcam.
You can now buy a decent dashcam such as the B1W for under $50, and a very decent one such as the A119 for a little over $50. Not many people will want to spend $150 for a small improvement so our 4K 100Mb/s H265 dashcam needs to be around $100 and that is currently not possible. Maybe the A119Pro can be that price with its 2.5K video, but we need to wait a little longer for a Novatek 4K processor that can do 100Mb/s 4K for $100 before 4K dashcams really make sense. I don't think the lens is a big issue, look at the sharpness of the B1W lens and it is obvious that lens technology has already improved considerably in the last few years with glass aspheric elements becoming reasonably cheap instead of hugely expensive.