I can tell you why it is recommended. Because those vowels are the most common. Such games you want to make a letter guess as close to 50% as possible (all letters including vowels appear less often than 50% of the time).

But as I said they ignore that guesses are not statistically independent that is to say a word with an a and and e is suddenly much less likely to have an i. So once you learn about a and e from stare then you decide if you want to guess i o and u or not and what you will find is that in fact you HAVE to guess one of them unless you want to repeat a vowel just for position, not an optimal strategy. I have resorted to bizzare non words on guess 2 like lindy just because it has only one vowel and 4 constants that aren't in stare.

All in all some math guy but non puzzle guy came up with this adieu thing, which may give the most hits statistically but is not the best first guess.