an hero.

Because quest-items turn droppable if the quest they're needed for is ended. There are only some items which stay quest-items forever.

I guess it is so when they are no longer needed you can't move. But if elder scrolls can't be removed, why have weight values if they weigh nothing?

Tell me Why is the weight there in the first place then?

Incredible how many people are too stupid to realize that questitems don't weigh anything. So many useless mods out there trying to fix that.

Elder scrolls, like all quest items, cannot be dropped unless modded to do so or if the quest they are required in is done (elder scrolls and the nightingale journ can't ever be dropped). I have never checked to see if they have weights, as I always have a ton of heavy stuff on me and lots of extra storage.

Dawnguards Elder Scrolls are not droppable I completed the entire story line and was unable to drop any of them. they weigh 20 each.

They weigh nothing anyway. Quest items you cannot drop do not use their displayed weight. You can always get to 0 by dropping stuff.

Dawnguard can be turned off, it's a masterfile and plugin, like any mod (well, mods don't use masterfiles normally, but they use something functionally identical). I also never understood why elder scrolls weighed 20, couldn't be dropped or removed, but could be sold for a measly 6000 septims.