This is misleading at best.
AIX didn't exist for IBM to purchase. IBM collaborated with Interactive Systems Corporation under contract to develop AIX in 1985 and released AIX Version 1 in 1986. IBM collaborated with Locus Computing Corporation, again under contract, to release Version 2 in 1992. Since the mid-1980's, IBM has poured massive development into AIX, which got so stable and feature-rich that when IBM tried to switch to Linux prematurely in 2005, its customers' and their systems administrators complained until IBM's Linux deployment was shelved for nearly a decade in deference to AIX (5, 6 & 7), and never really went away; AIX is still under active development.