They did it to get into the high end workstation / midrange market. Remember that they also bought Tandon at about the same time, known for their fault tolerant systems. It did sort of make sense at the time, but then, this was the time when Intel processors began to leapfrog forward in processing power. NT was also designed to run on the MIPS processor, which was in the DEC systems, and those processors were so much more powerful than the Intel processors of that time.
Mark
Tandon builds tape drives. Tandem builds "fault tolerant" systems. When I was still at PacBell, we considered acquiring Tandem. It would have been a valuable addition to keep the IT shops up with fault tolerant systems. Tandem was excited about the new "non-stop UNIX". A demo was arranged at the San Ramon office. I couldn't attend due to deadlines, but my cohort in crime David St Pierre did attend. Tandem set up the machine and shortly thereafter the "non stop UNIX" stopped. It was down all day. It never ran while anyone of importance was present to see it. Suffice to say that we didn't proceed with the acquisition plans.