Why don't brushes that I import into Illustrator save in the library? I'll open a new file and they won't be there any more. Is there a way to make them stay in there permanently?
"You can make the brushes you create available for every new document by adding the brush definition to the New Document Profile"
If you want to "load" the brushes you saved, you click on Brush library icon and choose User-defined brushes:
To have the brush automatically load without having to import a new library every time, in Illustrator CC 2014:
1) In Illustrator, apply the brush to a path, then copy the object to the pasteboard (effectively copying the brush as well)
2) Go to your "New Document Profiles" folder
(for me it's: C:\Users\[yourusername]\AppData\Roaming\Adobe\Adobe Illustrator 18 Settings\en_US\x64\New Document Profiles)
3) Copy and rename any profile template you want to add the brush to (you CAN edit the stock profiles, but I'd strongly recommend against it.)
4) Open your new template in Illustrator
5) Paste the path, and look to see that the brush appears in the brushes pallet
6) Delete the path
7) Close and save your new profile.
To test, create a new Illustrator doc, selecting your new profile's name from the profile drop-down menu. Check the brush pallet. These instructions should work for other versions of Illustrator, but the path to the profiles may differ.