Solving an audio-only CAPTCHA with AI is typically way easier than solving some of the more advanced visual challenges. So CAPTCHA designers are discouraged from leaving any accessibility options.
Ban non-residental IPs? You blocked all the guys in oppressive countries who route through VPNs to bypass government censorship. Ban people for odd non-humanlike behavior? You cut into the neurodivergent crowd, the disability crowd, the third world people on a cracked screen smartphone with 1 bar of LTE. Ban anyone without an account? You fuck with everyone at once and everyone will hate you.