Complex sentence: In addition, the OSI protocols were specified by committees filled with differing and sometimes conflicting feature requests, leading to numerous optional features, because so much was optional, many vendors' implementations simply could not interoperate, negating the whole effort.
Split into simpler sentences: In addition, the OSI protocols were specified by committees filled with differing and sometimes conflicting feature requests, leading to numerous optional features. Because so much was optional, many vendors' implementations simply could not interoperate, negating the whole effort.