with a slight alteration...

It is true that while the strongest were the only ones able to use the weaves on a regular basis, i'm sure that they were all taught the weaves in OP School. Just like Soriela knows the weave for traveling but isn't able to do it.

Eventually the Strongest did die off, and all that was left were those that weren't able to produce the weaves. But they still knew them of course and when they were able to find those that could (whether to be trained or those that could already) they could pass it on. As mentioned above, Ishmael likely had a hand in it by hunting down those that were strong enough to learn.

Eventually though, generation to generation, while still knowing, can't use it. And if you don't use it, you lose it.

Think about HS math. Unless you still use it (still going to college or use math on a regular basis) can you tell me how to figure out a sine, cosine, tangent of a triangle by hand? or the Pythagorean theorem? Or HS Spanish? sure, you could probably figure it out eventually, but if you don't use it, you do lose it. So it is likely that over time, those that couldn't make it work to just let it slide.

In the Rhuidean Columns, it was shown that the AS that came to take things from the Tinker wagons was on the edge of sanity due to being forced into Survivalist Mode for a long time and in that mode, you don't hang on to those things that are useless to your survival.

Also, you may say that "well I remember those things and I could pass them off" but not everyone is an effective teacher. Could you truly teach others well? Could they? and those that they teach? And with those unable to teach effectively, new channelers couldn't be brought to their full potential as well. Granted, the "no strong enough" channelers is a plot device but it is a valid theory.