India is not even close to replacing the huge European middle class and even if it were it has proven to be a highly unreliable partner. And so far the US exports to India are not even 15% of what is exported to the EU (2022).
The EU middle class comprises around 280 million people. Almost as many as the whole US population. And it is culturally and politically aligned with the US to a large extent. It‘s a huge market to loose.
Nobody would drop 15-20% of their exports to try to save 5% of their defense budget all while loosing influence and power.
To reverse roles in your argument: Imagine if the US put sanctions on EU companies because EU militaries aren't doing enough to help the US fight cartels in Mexico. Seem reasonable?