Because he is smart? He is also a selfish ruthless liar, a sinner, a narcissist, and not a good man at all, however he is smart, he wouldn't become the president twice if he wasn't. Moreover, he is a chance for the US to change and rapidly rebuild itself for future (multipolar world) and if I was American, I'd surely support him.
It works for the populus. He's a populist politician after all
Politicians lie. That's what they do. That doesn't make stupid
Okay. Let's dive into this situation. What did Trump want from Ukranian conflict 6 months ago?
First, he needed money and resources for the US and Israel, so he stopped the aid to Ukraine and diverted it to Israel, then got rare earth elements from Ukraine in exchange of it, and some time ago he literally made Europeans pay for new aid, which is reviving American military industrial complex at someone else's expense. He's done what he wanted. Futhermore, when Ukraine is to make deal with Russia, he'll be able to give up Ukrainian land in exchange for something from Russia. Brilliant.
Second, (the part that he wanted for himself, and not for the US) as an old man, he wants to be seen as a good guy in history (and get the Noble Peace prize, just like Obama). That's why he either needed to make peace there or to get an excuse to distance himself from the conflict ('both sides are corrupted pieces of shit, America leaves'). You can see that he's chosen the first option, which is the hard one, because the war isn't ending that easy. You can see that he struggles with it, because he took a 50-day break ('I give Russia 50 days to declare a ceasefire'), so he can focus on other things, especially domestic ones. However I wouldn't say this fail of him is too important overall if I was American, because it has no direct consequences for America (as nation state) for now.