If you've already got it, why do you want it online as well?
Because when I am at work and want to see the map, seeing it online is convenient, as opposed to hauling the book around. I'm sure there are plenty of other reasons as well, mine and other people's.
And because I would like Mongoose to present their best materials. Why would they put the first edition online, but not the revised Atlantean edition? Updating it makes the most sense.