Same reason as why we're not developing starships to go to the other side of the Milky way at the moment: We don't know how to and the leap from "what we can do

Same reason as why we're not developing starships to go to the other side of the Milky way at the moment: We don't know how to and the leap from "what we can do right now" (ie we struggle to get people to the moon permanently) and "other side of the galaxy" is simply too big.