Why cant a spacecraft go beyond earths gravity?

The Earth's gravity is indefinite. The earth will always present a force on a spacecraft, no matter the distance. However, the force could become very very small with increased distance.

A space craft can go past the point where earth's gravity will not cause them to fall back to Earth. Some crafts stay in orbit, so they are still close enough to the earth to stay "locked" into its gravitational pull, but other crafts such as the Titan have gone very far beyond.

Any object with mass has an escape velocity. The escape velocity is the velocity at which an object must travel in order to escape the gravitational pull of the massive object. The escape velocity of the Earth is 11.186 kilometers per second (a little over 25,000 miles per hour). If an object can travel at that speed away from the Earth, it will travel away from the Earth and it won't be pulled back in.