Im sure some people with wealth and power have thought that. The only problem is haven't we seen this strategy repeatedly end up as the cause of war and conflict when one side gets cut off from a critical resource due to politics? Japan in WWII didn't really give a shit about the US except as a bottleneck to their supply of gasoline and oil. And im sure I could cherry pick out numerous examples throughout history.

Being self-sufficient prevents you from conflict both in preventing external politics from potentially cutting off from critical supplies, and by making the potential fruits of conquest and war fairly limited. Like who is going to go to war over 5% cheaper steel? You will trade for that deal, but likely not kill. But the trading could be part of the source of the problem because it can hollow out your own native industry over enough time, or prevent native industry from being built when it can be bought cheap.