Isn’t Kai Shek one of the most important founders of Taiwan? Sure, he had his issues (for example, ordering the deaths of a couple folks now and again), but you cannot have modern Taiwan without him. Just like how Mao is an integral part of the shape the modern PRC took.
Israel is currently the US’ closest ‘ally’ in the Middle East. Not that Israel wouldn’t turn on the US in a heartbeat, but the US needs Israel to maintain force in the region. Add to that, Israel is Jewish. In light of events almost 100 years ago, it’s a bit problematic to criticise anything a group of Jewish people do.
The US can’t exactly come out and say anything that would be too disruptive to their relationship with Israel.