I think the best way to answer this question is as follows: Technology in Traveller is old. The Vilani have been doing space flight navigation since before there was writing on Terra. So every possible combination of computer technology, software, and expert system analysis has been tried, and ultimately rejected. The reasons are subtle (i.e. way too small to show up as a +1 on the rolls, even using a d100), but the affects are real.
This explanation won't fly with players that have even average IQ's...