Companies won't pay enough for quality QA people, so you can't get good people to do it instead of a more lucrative dev position. So now everybody has to do testing, except they only want to do the bare minimum and they aren't as practiced at it so they aren't as good as someone with equivalent talent but more experience writing comprehensive tests.

Start paying "QA" more than their dev partners consistently and with better promotion opportunities and you can get better testing, but everybody seems to be making plenty of money without it.