The Sun contains 99.8 percent of the mass in our solar system. Its gravitational pull is what keeps everything here, from tiny Mercury to the gas giants to the Oort Cloud, 186 billion miles away. But even though the Sun has such a powerful pull, it's surprisingly hard to actually get to the Sun.
TLDR: Earth moves fast, probes need to go slower. To reach the sun, you need a lot of energy to cancel Earth’s momentum.