There's a common feature of massive complex projects the world over - they pretty much always come late and massively over budget. Then as infrastructure mostly end up sticking around for a century or more, sometimes limiting future choices.

Rail, tube and tram lines will still be there and graded 100 years later - after track replacements, roads are not dissimilar, reservoirs and storage caverns far longer with a turbine replacement or two. Nuclear on the other hand has a much more limited life in which to absorb those overruns.

What has this to do with bad project management? I do not see anything particularly bad happening in this project, while the BER is indeed a clusterfuck that keeps giving.

They are still within their financial budget for this project, will maybe overshoot it by a bit in the end. But that's OK, since such a dismantling had no precedence whatsoever, and it was just an estimate and everybody knew that. They will exceed their time budget by a lot, which is also OK, since again such a dismantling had no precedence whatsoever, it doesn't really matter if this thing takes a decade longer to dismantle, and the reason they take longer than initially estimated is that they had to overcome a ton of problems nobody could have known about before and went about their work carefully and systematically. There were a lot of lessons learned from this, which should help with being faster when dismantling other nuclear plants, but and a bit cheaper (maybe at 2/3rds the cost in the future).

With BER on the other hand the date of completion did matter, both politically and economically, and the exploding time and financial budgets were a result of gross incompetence in particular from the politicians that personally kept meddling in the project (it was "prestige" project), complete failure in contractor oversight (which resulted in a ton of defects and also some corruption and embezzlement) and a completely useless project leadership (of mostly political appointments, aside from the politicians themselves, that e.g. resulted in them building that thing without working fire safety).

But they should increase your bayesian estimate of typical project costs for these types of projects. If we had a way of reliably preventing bad project management such things wouldn't happen.

That some other projects were late does not mean much for dismantling a nuclear power plant, which is a very different/ unique problem with different actors.

Wind and solar projects are not coming in at 3-4x their costs anywhere.

So the fact that they are simply simpler projects which rarely (never?) have massive overruns due to "bad project management" is a huge financial point in their favor that is rarely factored in.

Indeed. A huge and complicated project is a much wonderful playground for involved people (from the planners to the decommissioners). They benefit from it (on all accounts, including intellectual, financial, reputation, tolerance for error...) much more than they would with simple and transparent ways.