system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass Effect] Why the stagnation in technology?

Most of the nonhuman races have discovered the mass effect relays centuries ago. But there have been very few technological advances for these races. Humanity quickly catches up to their level once they discover the mass relays.  
How come there seems to be this stasis?
gpt
"Your civilization is based on the technology of the mass relays. Our technology. By using it, your civilization develops along the paths we desire."
-Nazara AKA Sovereign

The Reapers have built an artificial plateau for the Galaxy to stagnate in. If a race continues advancing too quickly, then the cycle will simply cull them faster than usual.

Noticing this odd inactivity in the Galaxy is a case of survival bias. We are only alive to notice it because it already happened. It might be that the Asari and Turians were just very conservative in their research. If they had taken a crowbar to the first relay they found, the Reapers would likely intervene before they started building their own. Humans coming along may or may not have spurred the cycle, because we were much more aggressive than even Salarians in our pursuit of technology.