Question

Why is there a rich capillary network around all endocrine glands​

Answer 1

the hormones secreted by endocrine gland enter the circulation and are carried throughout the body to act apon targeted cells located far away from the secreting gland. that's the reason why endocrine glands are vascularized with small many capillaries amongst the nest of their cells

Answer 2

the hormones secreted by the endocrine glands enter the circulation and are carried throughout the body to act upon target cells located far away from the secreting glands. Thus, endocrine glands are highly vascularized with many small capillaries among the nests of endocrine cells.