The point is boys have a penis and they draw penises.

The penis has always been a symbol of fertility because it represents the seed. Semen in English translates to the Italian word seme (which means both sperm and seed) and, no wonders, it comes from Latin semen (pronounced /'se|me|n/), but the Latin word meant "from the same roots". In Greek it's σπέρμα (pronounced /'spέrma/), in Italian the same word is sperma, in English it's sperm.

From σπέρμα (seed) comes the Italian word speme, that means "hope"

In Japanese, Chinese, Sino-Tibetan, Vietnamese, the word is always related to "sprout" and "grow".

The Japanese kanji for sperm has two roots from Chinese alphabet, one means energy, perfect, the second means child.

MDMA is just a synthetic drug of this time and place (mostly the west), it doesn't mean anything for anyone.

So, while girls today are (mostly) free to express their artistic abilities, unlike the ancient past, they prefer to draw vulvas (in various forms from the most realistic to the metaphorical ones) and not dicks, because they do not have one.