My only theory is that weaves weren't shared due to channelers being isolated from each other or simply mistrusting those they did encounter. Thus knowledge disappeared as the AOL channelers aged and died.

It's still a stretch to believe that Travelling was among the lost weaves, however. It was broadly useful and doesn't seem to require a special talent. You would think every AOL channeler with sufficient strength would have learned it.

As Gher pointed out, making angreals and cuendillar weren't common weaves and probably required a certain aptitude. It's far easier to believe that knowledge could be lost.

Knowledge of Balefire would have been deliberately allowed to die out.

Compulsion wasn't actually lost, just forbidden. Besides, even if the AOL weaves had passed from memory, apparantly half of all wilders figure out some version of it on their own.

So Travelling is the only big mystery, IMO.