This is basically due to Google probably rightly believing that electricity price in Finland is going up due to all these datacenters and also a pr stunt that the current government loves because they can claim that they aren't allowing these datacenters to raise electricity price.

This isn't investing in power infrastructure in any way, there is no reality where that nuclear plant wasn't staying in operation as long as they can possibly keep it running in the foreseeable future. Basically only way Google and Fortum will be building new nuclear capacity is by Finland promising to cover any electricity price below 15 cents per kWh in the market.