A. Buy your cheap brushes at Harbor Freight. $5.99 for 36 brushes.
B. Don't do a very good job of cleaning your brushes. Not that these cheap brushes clean up that well anyway.
C. Instead of throwing them away, cut off the junked-up ends and turn them into cheap stencil brushes.
Harbor Freight is as much fun, if not more, than Home Depot. And a lot less expensive. I signed up for their mailings and everytime I get one I usually find something I absolutely must have or better yet, need. Some of Susan's birthday gifts came from Harbor Freight: Rattlesnake Eggs, a new lighter weight drill, and more chip brushes, because we all know who doesn't clean out their brushes.