All good courses are bound to deteriorate in quality. For tech courses, this is due to two main reasons:
Others adding things: If your course can be edited by others, most likely, they will add things that they think are missing in the course. Adding things will almost always make the course lose its original simplicity and lose effectiveness. It's human nature for others to want to add what's "missing" in the curriculum.
Do not ever expect that you'll create a course that will never need to be edited/updated. Just like when you plant a garden, you can't just plan the seed, walk away, and expect the garden to be flourished with amazing vegetables. A good course needs pruning also. It may also have been contaminated by foreign seeds. Similarly, a good course could have been contaminated by too much other content that were introduced by other folks who didn't fully understand your intent when you created the course.
Key Take Away
Accept that your course will probably need to be updated every 12 months or so, even after you've iterated multiple times and came up with what you think is a final version. Each update may be minor.
Do NOT allow anyone else other than the course author to make direct changes to the curriculum. Even if others have good intention, adding things to the course, initiated by anyone other than the course creator, will result in the course losing its original simplify and effectiveness.