Because the game was incredibly successful and other companies tried to copy the formula. The same reason a lot of companies tried to copy Fortnite or League of Legends.
There aren't ripoffs of Breath of the Wild. Maybe Immortals Fenyx Rising is inspired by BotW, but I can hardly call it a ripoff. It's a unique game that stands on its own. Otherwise there is no increase in Breath of the Wild ripoffs in 2020.
You mean, aesthetically, Shadow of the Colossus, Ico and the Last Guardian? The games BotW aped? And that's just aesthetically. BotW is every single Ubisoft open world dumbed down for children with a couple of garry's mod dodaads added to the mix. The execution and polish are top notch but there isn't a single innovative bone to BotW, there's ample refinement but nothing new. I invite you to expand your played games repertoire to include some of the ones I mentioned. Ueda is nothing short of genius.