"the elimination of the costs"? Umm. They'd have to produce twice as many charger cables, and produce more complicated, presumably more expensive charge ports for every car. There might have been some savings in not developing the hardware and the software by going with an existing standard - except that Tesla invested that money before CCS existed. There's no savings for Tesla there now.
There's no expansion to their network, either. It gives the cars compatibility with other networks being built by other people, true - but that's not at all the same thing, and as of now those networks are 2x to 5x as expesnive to charge on, so no one is likely to want to unless they hit a long, long delay on Tesla's network - an event made more likely by the switch, since it'd take resources Tesla could use to expand the network and expend them retrofitting existing sites.
It'd also mean that the Supercharger plugs fit most other brands of cars, so even if Tesla doesn't open the network to other folks, you'd see delays from all the confused people trying to charge - and if they do open the network, you'd have a bunch of other brands of cars that charge slower choking things up.
Tesla gains nothing from doing it, but it has the potential to cost them a bunch.
Why would this change require more charging cables. That is what they have to do now. One set for North America, one set for EU.
And expansion of the charging network would be real to Tesla owner. Tesla could update their Supercharging billing infrastructure to interface with Electrify America and provide charging on EA at discounted or free rates to the Tesla owner. This subsidized sharing would be cheaper for Tesla than build more dedicated locations since there are no additional land acquisition, building, and on-going maintenance costs. It would be similar to the way MVNO wireless carrier (Cricket, Boost, Republic, Straight Talk, Easy Go, Consumer Cellular) do not build their own infrastructure (towers, back hauls, etc), but rather use the infrastructure of existing carriers (AT&T, Verizon, Spring, T-Mobile).