My toasted couscous didn't soften properly. Why?
It sounds like it might have been fregola, a toasted pasta from Sardinia. It is quite similar to Israeli couscous. There is nothing wrong with the cooking technique you are using, I think you just might have found a brand/batch that isn't very well made. If there is a lot of unevenness in the toasting or size of the pieces, then that will likely result in an uneven cooking in the liquid. As you can imagine, the darkly toasted pieces have more of a shell that makes it slower for them to absorb water. Don't give up on fregola though, it can be delicious stuff. You can also buy regular Israeli couscous and dry-toast it in the pan for awhile before adding the other ingredients.