Because it's heavy (or massive, if you want to be pedantic). Last time I was there, I struggled to keep my test1cles from touching the floor of my spacecraft ...
weight was implied in the use of the word heavy. I forgot to mention when 'correcting' Squarebear that distance from the centre of gravity is also a determinant of weight as well as mass.
Blackeyed wrote "so all the planets bigger than earth have a higher gravity(than earth)?"
It's not size but mass that matters. A planet could be bigger than the earth but not as massive due to the density of the matter it was made up of.
So you could say: The more massive a planet is the higher is the force of gravity on that planet.
It is possible to have a planet with a greater mass than the earth that is a lot less dense so that when standing on the surface you would be so far from the planet's centre of gravity that you would weigh less than you would on earth.