Why doesn't the US attempt to walk on the moon anymore?

Answer 1

The Apollo missions used large, expensive rockets that are no longer being built: huge Saturn V and Saturn 1-B boosters that could lift into orbit the heavy spacecraft (and their propellants) needed for trips to the Moon. Only Russia and China are currently building rocket boosters of this size.

There was a plan in place to use the Orion rocket to establish a lunar base during the next decade, but budget cuts cancelled the program. Evidently the majority of US Congressmen would rather fritter away funds on programs that are less valuable, but that visibly affect their re-election chances.

Answer 2

The US currently focuses on other space exploration missions, such as sending humans to Mars and developing sustainable space technologies. The costs and risks involved in sending astronauts back to the Moon pose challenges, and there are scientific and technological advancements to be gained from exploring other celestial bodies.