It's still horribly expensive and slow to build.
https://en.wikipedia.org/wiki/Hinkley_Point_C_nuclear_power_... : approval in 2012, 50% cost overrun, projected completion in 2027.
People will counter that with various other reactor designs, but if it's a new design, it no longer counts as "proven", does it? Not until the first one is running.
Then there are two other risks:
- the "black swan" disaster, where a Chernobyl cloud takes out European agricultural production for months and in a few places years. Very low probability, but things can go wrong; the shelling near the Zaporizhia nuclear power plant, for example.
- nuclear proliferation. Everyone's forgotten about this since we're fine with the existing nuclear powers, but does that apply to every country?