The electricity cost is actually very low compared to the capital cost of the stuff the the electricity runs. But not having access to the electricity means that all that capital is going to waste.

So Microsoft is less price sensitive than other electricity customers.

Plus they get the PR and hype boost from saying they are using nuclear, which is huge right now. Which is big enough that the other hyperscalers thought they had to announce new nuclear projects, even though it will be a decade before those new nuclear projects could ever come on line.