Why do you think that the striker does not advance his position as well? The whole point of using angles and lateral movement is to give yourself a better than 50/50 position. Strikers do all kinds of things to put them in a position where they can hit the other guy, but the other guy cannot hit back. In doing so, they are putting themselves into positions of advantage.
If we are talking about a striker verses a grappler, and the striker can keep the grappler from grabbing him (like Silva, Holm and Nunez did) that is not a 50/50 position. That is a position where the striker can use his techniques to hurt the grappler, but the grappler cannot hurt the striker.
Strikers advance their position all the time. They have many ways to do so. It just looks different than advancing your position in grappling... but it is still advancing your position.
Both are trying to put the opponent in the place where they will receive the most damage from their techniques. If both are trying to put their opponent in the worst possible position, how is one a more aggressive attitude than the other? Yes, the positions are different, and the techniques used are different, but both are trying to break the other guy as much as possible. Both are aggressive.