Technology

The primary issue is that deuterium-deuterium reactions (the only practical fusion process that seems to work is deuterium-tritium and deuterium-helium, as you need insane temperatures for proton-boron, so in any realistic reactor deuterium will end up reacting with itself) produce 3 times the radiation of equivalent power output from fission reactions, so you need MASSIVE amounts of shielding for a reactor to run for an extended period of time.

This also highly irradiates the materials inside the reactors themselves, to a degree that maintenance requires built-in robots because the inside of the reactor is too radioactive for humans (this also eventually destroys the robots). The most optimistic estimates for how long a reactor could possibly last is 100 years. At that point the entire reactor would need to be torn down and buried because most of the components would be too radioactive to use anymore. At which point you have the exact same issue as radioactive waste storage, but no recycling process for something crazy like a radioactive isotope of silicon.

However! That's why these experiments are important! As every advancement they make towards making fusion safe, also makes fission safer, as they're two sides of the same coin.