Because most of what programmers do has no theoretical basis or system of proof, programmers back away from anything that looks like hard math. Failure to understand and appreciate relational theory has launched countless bad databases (and thousands of witless articles condemning SQL). The idea that there is a right way to design a normalized database–and that the wrong ways are provably wrong–is alien to most programmers. Database management doesn’t come down to a matter of opinion like OOP class hierarchies or coding style.
Most professional programmers know how it feels to see an amateur, unfamiliar with Knuth or any programming book containing equations, implement their own sort routine. That’s how people who understand relational theory feel when they see a badly-designed database. Relational theory and RDBMSs are old and well-established now, so it’s hard not to think a lot of programmers are willfully ignorant.