My opinion on this matter is that the Asgard Beam Weapons were newly developed technology.
The Asgard were having immediate troubles with their cloning system degrading with each use.
CARTER: There must be something more you can do.
THOR: I assure you, we are providing you with all the latest Asgard technology, as well as a knowledge base, including our entire recorded history.
CARTER: That's not what I was talking about.
THOR: Everything that can be done, has been done. The final attempt to solve our physiological degeneration has left each of us with a rapidly progressing disease.
Before then, they would have been focused on solving that problem, as due to their weapons being powerful enough to easily take out anything besides Ori motherships, they had no previous need to develop new and more powerful weaponry. As the saying goes "Necessity is the mother of invention" and until this point, they did not have the necessity.
They only would have tried designing new weapons when it became abundantly clear that they were going extinct and needed someone to carry on their legacy (they had no reason to believe the Ori would do that) and entrusting someone with your legacy means little if the ones you're entrusting it to are unable to prevent themselves from being destroyed. This meant that their focus drastically shifted from ensuring their own survival to passing on their legacy and ensuring the survival of the ones they passed it to.