The problem is that there is no filling in of gaps without lane changes that cause the congestion. Everyone is making what they perceive to be the optimal move for them: "I'll just change over to that lane, because there's open space there and this one's going slow," but that individually optimal strategy isn't optimal for the movement of traffic as a group.
You don't even need to maintain large gaps - you just need about two seconds of time between you and the car in front of you, and that varies based on the speed of traffic. Everyone going ~30mph with gaps is going to have a lot more throughput than everyone averaging 10mph with short gaps. Of course this is before you get into the increased risk of collisions with smaller gaps. One fender bender is enough to bring everything to a halt, and statistically with enough cars and short enough gaps those are basically guaranteed.
Yeah, try setting your nav from Los Angeles to Irvine or San Diego to Irvine on any given day. Guaranteed 2-3 wrecks, plus some jams that the nav might think are wrecks but are just phantom jams.
You don't even need to maintain large gaps - you just need about two seconds of time between you and the car in front of you, and that varies based on the speed of traffic. Everyone going ~30mph with gaps is going to have a lot more throughput than everyone averaging 10mph with short gaps. Of course this is before you get into the increased risk of collisions with smaller gaps. One fender bender is enough to bring everything to a halt, and statistically with enough cars and short enough gaps those are basically guaranteed.