Good question but you might just as well ask why Windows not Mac? I'm afraid Microsoft have got a stranglehold and since AOL have virtually abandoned any further updates on Netscape I can't see it lasting too much longer.
I think Microsoft have about 95% of the Browser market and all the others share the remaining 5%. As greysts says Netscape appear to be giving up the fight by laying of their staff and hence no up-dates in the future.
Once, during Prohibition, I was forced to live on nothing but food and water. - W.C. Fields .