because you can easily make a half-blood farmer out of it.
For the most part, half-blood farming is a waste of time. The chance of winning an upped card is low and the gaes take a long time. Over time farming AI3 with a speed deck > fighting AI5 with mono aether.
Aether is a great PvP element, but generally a terrible choice for a beginner imo as it earns electrum much slower.