Some caveats on this:
a) That is only proven reserves, there is much more to explore, so you cannot categorically say so.
b) Just a few years if used exclusively and if Europe does not reduce gas dependency, both of those premises are questionable.
c) Enough to not depend fully on Putin in case of war. It is about strategic independence and having an additional supply that can be developed with funds from the West.
And, as others said there are many other reasons and resources, including some related to the supply of food to China. A video I found is interesting to understand the wealth of Ukraine and the repercussions for the international geopolitics.
Unless you think that this is really a Nazi hunt as they say?
I rarely post videos nor see videos from other people's post, since most of the time they are intended to increase the algorithm ratings of propaganda , but this one is very illustrative of the true reasons behind this aggression and is relatively neutral, just states the strategic contex.
https://youtu.be/BftqoZOryDo?t=629
It even explains Chinas yes / but no / but maybe position.
The bit that bests responds to the reformulated strategy would be here:
https://youtu.be/BftqoZOryDo?t=889
...
The numbers, a bit more accurately:
Reserves(without further exploration): 39 trillion cubic feet
Germany consumption: 3.13 trillion a year
39 trillion cubic feet / 3.13 trillion cubic feet per year ... slightly above 10 years worth if used exclusively and if Germany does not reduce dependency on gas and if no further reserves are found.
Seems like this is a important reason for what's happening, I reckon not the only one.