Part of the reason for this was undoubtedly their vendor-independent approach (see Unix wars).
While the converged Unix from the Sun and AT&T alliance (that spawned the Open Software Foundation or OSF), released late 1986, put BSD features into System V, DEC, as described in Stettner's original Ultrix plans, took the best from System V and added it to a BSD base.
Since then, occasional bursts of Unix factionalism have broken out, such as the HP/SCO "3DA" alliance in 1995, and Project Monterey in 1998, a teaming of IBM, SCO, Sequent and Intel which was followed by litigation (SCO v. IBM) between IBM and the new SCO, formerly Caldera.
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