This is what I don't understand at all. Imagine somebody in a different area of computing would say: oh, we solved that 30 years ago and now there is no room for improvement at all? why can't this be done at least in C?
There is room for improvement, and it gets improved all the time (e.g. openblas is a recent contender). LAPACK is essentially an API for linear algebra, which is what allowed people to improve implementations and to benefit from them in older programs.
Think of it as the C library of numerical computing.
I was comparing LAPACK to the C library: nobody claims it is weird to use the C library, written > 30 years ago, instead of using something 'more modern'. Everybody uses the C library for system/low level programming, the same is true in numerical computing w.r.t. blas/lapack. Numpy/scipy use it, R use it, julia use it, matlab use it, octave use it.
Think of it as the C library of numerical computing.