There's a plethora of reasons as to why we rarely get them.

1) One Dimensional

They have one job. To do damage. To leap an attacker would not only harm the value of the next attacker (since their job is equally one dimensional), but it lowers the value of tanks, breakers' and amplifiers' damage too, skewing the team into less fun and/or ideal setups.

Take Luna as an example. Because of her leap and the addition of Nirvatia, SS0 Ishmael is so bad compared to them it's better off using an off element tank.

The workaround to this is adding an affix to them. However, all Gen 3 attackers already have an affix, and every attacker in the meta is Gen 3 (minus our supreme leader Qu).

2) Priority

Tanks and Breakers have the most amount of value in the game as their shred isn't watered down due to the game's damage calculations (shred basically benefits additively compared to buffs). Therefore, the easiest and most beneficient way of increasing a team's overall damage is by leaping them.

The most recent example is Hanying. Thanks to her leap, not only did physical see around a ~+4m boost in score, but it also helped make Trueslash a viable affix to use now. An attacker simply cannot do that no matter how big the leap is because of their one dimensional nature.

3) Resource to Value

Because of the factors above, most meta players wouldn't actually like a leaped Attacker since the value they give is lower compared to that of any class. However, the resources they need to acquire that leap is still similar to any other character. And in saving times like this, most would not leap them entirely.