BL anatomy

I want you guys' opinion on how bl writers draw their characters. Usually the top's dick is so big that it should be considered a disability (not making fun of disabled ppl btw). Not just their dick either, their entire bodies are exaggerated out of proportions (I read a bl where the top's neck would get larger and larger each chapter )

And the bottom is usually tiny and 'fragile' like a prepubescent child, why is that?