The vague answer is because the question not posed correctly, just as in the Australia/Britain up/down case.Question of whether Britain is up or down from Australia can be answered by simply posing the correct question and that is, from what vantage point? Can a physicist answer the question of whether an electron is a wave or particle from a given vantage pointe? I submit vague answers simply means The physicist providing such answers has not solved the problem.
The words “particle” and “wave” were introduced many years before the theory that we now call quantum mechanics was hammered out in the late 1920s, while it was still mistakenly (although understandably) assumed that those concepts would explain the surprising non-classical phenomena that were being observed at the beginning of the 20th century.
So there’s no clear answer to the question about whether an electron is a particle or a wave for the same reason that there’s no clear answer to the question of whether a sheep is more like a pillow (because it is soft and fuzzy) or a table (because it has four legs). If you want a clear answer about sheep you should ask what a sheep is instead of investigating the “paradox” of a sheep’s table-like and pillow-like behavior, and if you want a clear answer about electrons you should ask what the theory says about electrons instead of demanding that they be explained in terms of waves and particles. The difference is that we’re all familiar with sheep while many fewer people have put in the (seriously non-trivial) intellectual effort required to understand the behavior of electrons without recourse to familiar notions of waves and particles.
Two posts above to which you should pay particular attention:
1) @PeroK #23 where he points out that wave-particle duality doesn’t appear in modern textbooks (and the same is true of the QM texts I studied 40 years ago, so this is not exactly a new development). This should suggest to you that your understanding of what QM really says about electrons is not based on completely reliable sources.
2) @Demystifier #4 where he points out that we feel no need to ask whether phonons are waves or particles. There’s a serious question there for you: why do YOU believe that discussing electrons as waves or particles is necessary, but not phonons? There’s a historical reason why we do: electrons were known and discussed before the wave-particle duality notion was abandoned whereas phonons were not; but that tends to suggest that the wave-particle question is indeed badly posed.