Here's why:

* Epithelial tissue is specialized for covering surfaces and lining cavities. It has a high capacity for secretion, which is essential for the function of endocrine glands.

* Connective tissue provides support and structure, but it's not primarily involved in secretion.

* Muscle tissue is responsible for movement and doesn't have the secretory function of endocrine glands.

* Nervous tissue transmits signals, but its role is different from the hormone production of endocrine glands.

Therefore, the origin of endocrine glands can be traced back to epithelial tissue, which has the necessary characteristics for their function.