This is something that has always bothered me about Skyrim, and bows.

Little background first.
When I started making bows for Oblivion there wasn't any exporter for any modeling program that could export the animation needed to make bows move in game.
I racked my head trying to figure out how spending hours inputting x,y, and z locations of vertices by hand (literally hundreds of them for each model) but failed to get them to work in game.

Along comes Windy who figured out how to trick NifSkope into thinking two models of the same bow (one at rest, and one morphed) were the same bow, and having it draw the animation between the two of them for you.
Thank you Windy!!!!!

Bowmorphs that Oblivion used would allow for an even curve along the entire mesh so it was rather easy to get the bow to bend in a way that looked good in game using that game engine.

Skyrim uses a skeleton, and rigs the mesh to the skeleton much like clothing or skin is done.
Vertices are weighted depending on how attached they are to a bone in the structure.
The animation moves the bone structure, and the vertices follow the bones based on that weighting so that things like elbows, and knees bend in a way you would expect.

Now think about the bows you find in stock Skyrim.
All are fairly flat front reaching up, and down from the handle with limbs at the ends slightly bent back.
The bone structure was created for this basic shape and most all of the bows in the stock game follow this template.
The only one that doesn't is the wooden bow which is a curved shape like a traditional longbow.
Go grab one. Draw an arrow, and hold it. Now pan around and look at how it is bending because of how it's rigged, and the bone structure it's attached to.
Pretty ugly eh?
Lightening bolt bow LMAO.

Most of all my bows before this one have been static and 100% rigged to the midbone except for the string to avoid this lightening bolt shape draw on a curved bow shape.

For the Rivendell bow I decided to do something a bit different and work within the confines of the game engine while still producing something I would be happy with.

By loading the draw animation along with the bone structure, and model I was able to initially weight the vertices using envelope method then come back in while playing through the animation to change the weighting on small sets of vertices at a time smoothing out the shape for an end result I could live with without having a static model.

Labor of love really, and I am very OCD (Ask PhatBassAnchor...he can tell you).

Enjoy version 1.1 of the Rivendell bow with proper rigging nit picked  to death by me.

Have fun
Nico