Because uranium is cheap, so why bother? The price of nuclear energy is dominated by the cost of building the reactor, not the fuel.
The reactors he presented appeared to be much simpler (so... they'd likely be cheaper).
The industry dismissed liquid reactors because of the problem extracting weapon grade material. Uranium based reactors where not as safe nor as cheap. During the cold war this made sense but not today.
It has also been about people protection their jobs. The uranium based industry can't say that something else is better because then they might lose their jobs. And who do you think the politicians ask when they want advice?
Or perhaps you've been swept up by the breathless prose of popular science articles?
As far from peak uranium as we appear to be, there is simply no need to explore alternative fuel sources. Fuel is not scarce. The capital (political and financial) to build infrastructure - both power plants and reprocessing plants - is.
In that climate, the (never-been-built-or-licensed) LFTR is only a game-changer if its construction (and licensing and R&D) costs are an order of magnitude lower than those of current-gen reactors. This I highly doubt.
(To be more specific, it's the absence of nuclides with mass number greater than 238 in Thorium waste that makes it less problematic than Uranium waste. These nuclides dominate the long-time, i.e. millenium, radiation profile of the waste. The short-time, i.e. decade/century, radiation profile of the waste is dominated by lower-mass-number fission products, abundant in both types of waste)
Reprocessing plants are extraordinarily expensive to build and operate, more so even than reactors themselves.
And the cost of fuel is still important, uranium isn't getting cheaper.
And what calculations are those?