Because realistically, they've been dependent on fossil fuels for so long and the public for a large part have not been that friendly to renewable power sources for so long. Also, renewable energy hasn't been that reliable in the past. It's not like they weren't dependent and then decided to become dependent. And fossil fuels are a resource for which not many countries have it, so creating backup supplies isn't as easy as in other things.

Germany was about to build a backup gas pipeline (Abeit still to the same supplier), it took 10 years to just to get it to the viable stage before it was cancelled.