I hear in my headset "Clear for the option runway two-five-right, number two behind a cessna, two mile final, on the go make right traffic" and I know exactly what is expected of me without having to look at a screen. A digital display would be a step backwards.
EDIT: I will add I get that adding something like that to a general aviation cockpit is much easier than putting it on a commercial 787, but that doesn't mean we shouldn't try.
If anything, the helicopter needed more avoidance technology from the sounds of it. And that has more to do with the lack of integration the military does with civilian systems.
But there are tons of flying general aviation planes that are from the 50s/60's, and a long tail going back even further than that. Some of them don't even have a radio to talk on. Or an electrical system to run it.
Mandating ADSB took many years, and still has exceptions carved out. And that's a fairly simple technology. There are companies that build it all into a replacement tail light LED "bulb" to provide compliance for ~$2000.
Still that might be 5-10% of the value of your 1977 Cessna 152. If you take the cheap airframes out of the sky, that makes new pilots getting their 1500 hours more expensive before they can go get a job on the big boy planes.
Audio makes perfect sense as a backup, but 99.99% of flights would benefit from having a screen showing object and current planned route.
In this particular case, simply having that information available would have allowed an onboard computer to predict a collision.
If a plane loses comms there are well defined procedures and everyone knows exactly what that plane will do as they proceed to their destination.