In a word, hubris. MSFT did the same stupid thing when they acquired PhoneFactor (which was currently in litigation with SFOR for infringment). Huge companies like Cisco think they can steamroll or wait out (in court) small caps like SFOR. To its' utter amazement, Microsoft failed and had to settle with us to the tune of $9.7 Million.
IMHO Cisco will meet a similar, but much worse fate financially (treble damages) once Ropes and Gray gets done with them.