>>718559351
I think it comes down to various factors.
>People being tired of Chinese and South Korean games especially Mihoyo(initial audience)
>People who played it for novelty reasons and ended up really liking it(this pushed it to the moon)
>Those who wanted a JP led Gacha that was not FateGO
>Finally those who watched the Anime a few years back and were waiting heavily for the game to come out
It pretty much created this huge pent up demand and Umamusume happened to satisfy everyone's desires. America also has a huge Horse Racing culture and other parts of the world have had appreciation for Horses in Europe so it really caters to these audiences overall.