Why invest into something that will only last 100 years in fuel, take 30k years to deconstruct and may blow into your face at every point in time. Sounds insane.
May as well ask why we use wind turbines when they might take off and start dropping napalm.
They can and they do (see: Chernobyl, Fukushima). But it's not a nuclear explosion (as you say, it's not possible with their fuel enrichment and geometry); it's a steam or hydrogen explosion.
But there are a lot of people who think a nuclear reactor can level a city, which is totally impossible.