The details of the proofs are perhaps not relevant to a practitioner. Although I trust you would agree that the existence of the theorems are very useful?

You seem to have the idea that the only useful thing to come out of linear algebra are a set of algorithms, and that as long as you have computer routines implementing those algorithms, the proofs that those algorithms work don't matter. There is a grain of truth in this, but the concepts that you learn in a linear algebra course - particularly around eigenvalues and eigenvectors - are very important in providing you the knowledge to choose those algorithms well. And the process of working hard to understand proofs is a great way (perhaps the best way) to make sure that you really understand those concepts. It's also a great way to make sure that you really understand what a theorem means / why a particular algorithm works.

most research is about speeding up calculations on computers

A a large amount of progress in "speeding up calculations" comes from algorithmic advances. These advances aren't being made by people who view linear algebra as nothing more than a set of library routines. They come from people who deeply understand the concepts and proofs behind the important theorems of linear algebra.