Bullet drop

In real world military-grade weapons you don't need to engage in Arkansas elevation, so long as you haven't exceeded it's maximum effective range. The M-16 for instance has an elevation knob that you can adjust depending on your range to the target. It adjusts the rear sight to compensate for range and the bullet's trajectory.

In layman's terms you wouldn't need to raise the sights above the target.

On that note this seems like a bit of a step backwards for Mass Effect weapons, so from a purely lore perspective it is kind of dumb.

In the end though when it comes to the shooter gameplay the only thing that matters is how fun it is, and this could end up being a fun mechanic.