It's not _on_ American streets. I lived in the US for 20 years and I've never seen one. Likely some SWAT teams purchased them for pennies on the dollar, but I'd argue SWAT teams need them, to reduce casualties when getting close to violent action.
> assault rifles
To the best of my knowledge assault rifles are not in use by US police. AR15 is not an assault rifle.
I saw plenty in London though.
But that's nuance - people younger than, say, 35, won't understand any of it. Literally nobody is interested in the actual reform at the moment. If they were, we'd see some serious proposals by now.
Check yourself, pot, that's an awfully broad brush to be calling a kettle incapable of nuance with.
https://en.m.wikipedia.org/wiki/Assault_rifle
https://en.m.wikipedia.org/wiki/Carbine
You may be confusing "assault rifle" and "assault weapon" which are different categories. The AR15 does usually qualify as an "assault weapon". The definition of assault weapon is looser, and includes a number of features (such as barrel shrouds and flash suppressors") the sole purpose of which is to make the gun safer to use, and have nothing to do with making them actually more dangerous.
https://en.m.wikipedia.org/wiki/Assault_weapon
If you have different sources, feel free so share.
Also, barrel length is one of the most common theme in firearms bans. Usually those consist of legal limits on the minimum barrel length in an effort to prevent people from concealing it, I guess.