But these browsers have one great feature: They give a very good indication whether a page is worth reading. If these browsers don't display anything, or the display looks shitty, there usually is not much content, either (In a few cases I looked up the page with something more advanced (e.g., Arena), and I was always disappointed).
In contrast, first-class sites like Altavista are very readable even with ancient browsers.
Why is this? Well, as Bernd Paysan puts it:
Die Featuritis ist meist umgekehrt proportional zum Inhalt, und wer Inhalt hat, legt in der Regel Wert darauf, auch gelesen werden zu koennen.(BTW, if you have something worth reading, You may want to process or check it with one of D.J. Delorie's HTML Authoring Services; there are also other web page evaluators; looking at the page with an ancient browser on a B/W screen is also a good check).
(Featurism is usually inverse proportional to content, and those who have content generally value being readable).
Apart from this practical reason, there's a principal one: The first time I invoked Netscape, it said that it is obsolete and refuses to work. I don't use software that thinks it knows better than I when I should stop using it. Actually, this is also a practical reason: Who knows whether a new version will be available and usable when the current one stops working?
If you have become interested in x-mosaic, you might be interested in further pointers and installation instructions.