There are several reasons that people stop creating.
1. Doing things that are harmful
We are basically good, even if we do wrongheaded things some of the time. The best proof of this is that people stop doing things when they realize these actions are harmful to others or to themselves.
It might take years for the truth to sink in, but eventually a person realizes that he or she is hurting others by doing something unethical and they stop doing what they are doing.
This happens frequently in the field of Marketing and Sales. A person uses their talents for many years to skillfully persuade customers to buy services or products and they discover eventually that the customers are being harmed in the process. This discovery makes it almost impossible to continue using that talent. They say they are "burnt out" and it can be a permanent condition if they do not find some worthwhile cause to support.
2. Becoming convinced by others that creativity is harmful
People want to create and they want to help others in the process, if they are of sound mind. Occasionally, there are people who have been so mistreated and so abused that their idea of creation is to punish others or to destroy what others are creating. They eventually become fixated on stopping others. They specialize in creating stops.
Most people are happy to create new things and new ideas whenever they can. When they run into people who are "stoppers" they may have difficulty continuing their usual patterns of happy creation. These "stoppers" will work very hard to convince creative people that they are "wrong" for trying new things, starting a business without years of experience, yada yada, and so forth.
The test you might want to apply is to look at what these stoppers have ever done that is worthwhile. Who have they ever helped? What products have they produced for the community? What organizations have they volunteered for?
3. Feeling there is no purpose in creating further
If your creative activity is driven by necessity, you may find that you approach creativity like a man using duct tape on life. Do enough create to put out the immediate fires and slump back on the sofa and watch TV again.
If your creativity is only done to kill time, like filling out crossword puzzles, it is doubtful that you are energized by the activity.
If you do not create for the purpose of enhancing another’s life, you may find that you do not derive any benefit from creating. Writing and sketching, even knitting or photography can produce beautiful results which are lost when stashed away and not exchanged with others.
A possible solution for those who feel they cannot be creative
Sharing or exchanging your creative activities can open up your life and can produce a great deal of happiness for you and for others. If you feel that you are stuck in a non-creative rut, try finding out what others need and want and you may find that your creativity is re-energized again.