Is anti-angiogenesis (angiogenesis inhibitor) part of treatment for cancer or not? if not why?

Possibly: Depending on the type of cancer, anti-angiogenesis may be used. For example, with some primary brain cancers, Avastin (bevacizumab) is an angiogenesis inhibitor that has reached fda approval status. There have been some other cancers where it was thought to have benefit initially, but then was shown not to be efficacious.

For certain cancers: Anti-angiogenic therapies are used in certain malignancies. Whether or not these agents are used in the treatment of a given cancer is based on preclinical and clinical data. Some solid tumors seem to respond, while others devise a way to to become quickly resistant. There are many drugs of this class that target different pathways, and many clinical trials are currently being performed.

Yes: Angiogenesis inhibition is probably the fourth most important field of cancer treatment after radiation, chemotherapy and surgery. See, for example, treatment with Erbitux and temodar (temozolomide).