It's because safety wasn't the obstacle to nuclear energy, cost was.
Also, I don't think passive safety of CANDU is what's meant by passive safety of HTGRs. The latter can survive losing cooling and everyone just walking away (in theory); I suspect the CANDU melts down in that situation, even if the chain reaction does stop.
Dealing with nuclear waste is still a thing, even with safe reactors. Here in the US, we can't seem to find a permanent place to bury waste.
Don't forget, either: Nuclear waste isn't just spent fuel. The reactor core remains radioactive after the plant is decommissioned.
That's one of the things that nuclear fusion proponents seem to forget. Even without the spent fuel problem, fusion reactors still produce nuclear waste.
That is very expensive. Given that they came online in the 70s and early 80s we can assume the initial capital investment is paid off by now and that cost is only the marginal running cost. (OPEX)
Now, currently we are building solar farms in desert areas for ~1.5 cent per kWh. Including both CAPEX and OPEX. On-shore wind is built at ~3 cents per kWh and ~6 cents per kWh for off-shore.
This is where the explosion of renewables is coming from, they currently undercut the marginal cost of traditional power sources.
Also, I don't think passive safety of CANDU is what's meant by passive safety of HTGRs. The latter can survive losing cooling and everyone just walking away (in theory); I suspect the CANDU melts down in that situation, even if the chain reaction does stop.