Why are computer science related degrees at some good European universities not ABET accredited?
I have not found much value in accreditation; it may serve to identify poor-quality schools, but most decently ranked departments sail through accreditation without any of their real deficiencies being exposed.  The process is thus little more than a bureaucratic checkbox for government or company sponsors of students.

If you want to gauge the quality of a department ... look at where its
graduates go.  What companies hire them, what universities accept them for graduate school/academic positions, what are their successful graduates doing 10-15 years after graduation?