I keep getting superficial mucoceles in my mouth. What is the cause of this? Is it a sign of a more serious disorder or disease?

Local irritation. Mucoceles are merely blocked ducts of minor salivary glands. The most common cause is local irritation. I have never heard of anyone having anything of medical origin to cause chronic and frequent occurrence. However, without actually knowing your medical and dental history and not being able to confirm that what you have are truly mucoceles, i cannot be sure. See your dentist or oral surgeon.
Explore further... It is worthwhile to research the cause with your dentist or oral surgeon to verify there is not a bigger problem. It may be due to a habit or tendency and resolve if this is addressed. It's possible (but less likely) for it to be a bigger problem. There is however, a higher probability, you may find a solution that makes your life better (or at least better informed).
Must be seen to know. Who made the diagnosis of mucoceles ? They are clogged ducts of minor glands that cannot drain. Someone -- a dentist or physician. Needs to see you.