There are several reasons. First of all, Vegeta is the little prince of Saiyan. Obviously, his pedigree is very pure, which is no problem. The Monkey King was randomly sent to other planets because of his impure blood. Originally, he was going to plunder the earth, but the Monkey King didn't do that. After a series of trials, the Monkey King can even beat Vegeta.
Secondly, when the Monkey King later fought against Felisa, his father was recognized by the other side as a Saiyan who fought with him to the end. Visible the Monkey King's lineage is also very pure, otherwise it is impossible to look exactly like his father, so the Monkey King's Saiyan lineage is no problem.
Therefore, Vegeta is a prince, so his pedigree must be very pure. The Monkey King is probably his father. To protect him from being killed, he was sent to the earth. So they are almost the same in strength and descent. Besides, when they beat Buo, they showed great blood power!