Interviews measure a shibboleth with a glancing relationship to relevant skills, which is more based on expedient and clever solving of the toy algorithms problems you'll find in college than the actual quality of a developer's output. Different companies' interviews attempt to measure the same skills in different and subjective ways, yielding different results.

Centralization on an evidence-based standardized test for the "prove your skills" part of the interview process is one of the best outcomes we can hope for. Ideally it would be open to non-degree-holders. Include per-component scores so companies can choose which areas they care about more, avoid grade inflation so similar candidates are distinguishable, etc.