I'm not saying they draw yuuri big too to the same extent, people love overemphasizing Victor as the stereotypical seme dynamic. They don't even have to draw him that way either, they just bastardize his character in their doujins. It was more of a "also its funny when they need to make the top bigger at all costs so when they make Yuuri big its doubly hilarious" thing. What is more common is when they do the reverse and make Yuuri tiny.
I don't know how common the ratio would be, but there's several artists that are fairly popular who do it. Like that one ABO artist. There's also that doujin of a drunk and buff Yuuri furiously power-bottoming, which I don't know how that fits into the scheme of things.