But why does china still use them during OA?
OA was a sim based on a past event, the "tanks" were mining rigs jury rigged with armour and boosted power to the laser drills.
However I see no reason pro or anti as of why tanks would not be in the FO world itself.
However, it took one heavily dedicated man to restore one car in FO2, even then he needed help.
Caravans if NCR had the ability to run fleets of vehicles caravans would not be needed as they are now.
Tanks still require roads or suitable terrain to perform at their potential, craters, ruins, heat and lack of infrastructre would not lend to their long term survival imo.
I see the NCR trying to build up something but as it is more likely vertibirds, trains, power armour and robots would be the aim as the tech seems more within their reach imo.