I mean, yes - if your biggest external source of energy declares war, and your hitherto trusted defence partner goes rogue - it's going to have a chilling effect and the measures needed to address that will hit both the economy and the populous
If you have 300 froblets per month being shipped to you, and suddenly you have only 200 froblets arriving and you have to spend £5 billion building a froblet factory, then you're both going to be short on froblets and high on expenses at least until the factory is built.
And yes, in the long run you'll have built the factory, will be getting a safer supply of froblets, and everything will be sunshine and roses, but while you're building it all that's an extra expense that you have to find the money for.
The money is spent on something and comes (hopefully) with a positive RoI and NPV. And you could borrow to build to reduce own capital outlay.
I don't think there was a lot of new energy production was put into place, though.
And spending money on one thing means you don't have it for something else. Even if you're borrowing, you can borrow less for other things, unless you want to break your credit score, which would also hurt.
I don't think Europe was anywhere close to borrowing capacity, so plenty of scope there.