"Why is cleanup so hideously expensive?"
The problem was never the reactors or waste products, which can be simply shovelled into the nearest convenient tectonic subduction zone. No: the real problem, which governments have tried to hide over the years, was the giant lizards, insects, etc. that rampaged through small villages and towns.
Unsurprisingly, the insurance premiums shot right up because of all that mayhem, making nuclear fission uneconomical.
As a PhD in Pure & Applied Comparative Conspiracy Theories*, I can assure readers that there is ample documentary and film evidence -- most of it produced in the 1950s and '60s -- to support my thesis. Some of it can even be found on YouTube.
* (From Oxbridge Dubious University.)