ABET accreditation is important in traditional engineering disciplines (e.g. CE, ME, EE, ChE) which are subject to state licensing laws. Virtually all reputable programs in these disciplines are ABET-accredited, because they know that at least some of their graduates will seek licensure. In practice, it is difficult (and in some states, impossible) to obtain a PE license if you don't have an ABET degree.
But Biomedical Engineering is completely different. BME is basically unregulated: there are no states that license biomedical engineers, and there are no biomedical FE or PE exams. So in practice, it doesn't really matter whether a BME degree is ABET-accredited or not.
For this reason, many prestigious engineering schools have not pursued ABET accreditation in BME. Examples include Cornell, MIT, and Stanford. These schools have ABET accreditation in traditional disciplines (where it matters) but not in BME (where it doesn't). UConn is the same way.