Compared with gas turbines? The main reason power is supply constrained is that gas turbines are a precision high-tech product that fails catastrophically if you don't build it right and maintain it.

Bloom fuel cells are a plausible alternative, but they are in the process of building out their manufacturing capacity, and operating experience at data center scale hasn't been tested. Bloom's process also involves extremely high temperatures, which could result in uptime and maintenance issues.