Or maybe because it's a huge, intensely competitive market where multiple top-tier companies are trying to draw users from each other: Microsoft, Apple, Google, Facebook, Yahoo. You can't stand still and expect your user base to keep growing. You might make your current users unhappy sometimes, but the goal is to keep getting new users, not just hold onto the ones you have.
the goal is to keep getting new users, not just hold onto the ones you have
I understand that this is the current goal of the companies you named, but, to put it bluntly, why should I care? My goal is to not have to deal with change just for the sake of change, or because some company wants to keep capturing new users. (Which is why, as I've said in other posts in this thread, I don't use GMail, don't use MS or Apple products, don't keep upgrading my Linux desktop just because somebody invented a new UI, etc.)
Also, "keep getting new users" isn't a sustainable goal anyway. Facebook already has more than a billion users; they don't have too much further to go before everyone that has Internet access at all (apart from a few outliers like me) will have a Facebook account. What do they do then?
