>>1121218625 years or so,
There's only a few countries (U.S., India, Brazil) who have large Thorium reserves. Yes, lower concentrations of Thorium are more abundant, however it is not all the economical to exploit it.
Gen III+ (and upcoming Gen IV) Uranium reactors are also proven to be incredibly safe and efficient, so that's why there's hasn't been that much effort to research Thorium reactors, since there's still a huge amount of Uranium left to exploit.
