Because subsidy is an idiotic way to fund it. What's the point of seeking private investment if the government guarantees profit, selects the reactor design and it's location? What usefull funcrion do private investors fullfill, their funding is more expensive than a government loan.
They should contract EDF to build it for a fixed price, job done.
The point is that it motivates the builder to complete it in a certain amount of time, not just at some time in the future. However, that induces too much risk apparently.
In the US most contested have been for a fixed price, it's just that nobody meets that fixed price nor the schedule. And since nuclear front-loads 50 years of generation prices into the construction, Amy delay at all I'm starting service is a financial disaster.
They should contract EDF to build it for a fixed price, job done.