>Except it's not. Remember how everyone switched to Altavista in 1996 because it was so much better? Remember how Yahoo took over in 1999 because it was so much better? Remember how people switched to Google in 2003 because it was so much better?
You already have the answer here you said it 3 times - 'so much better'. People switched because it was 'so much better'. Not on par, not slightly better, just so ahead of the competition, it became a talking point all on its own.
If this mass isn't reached then why would you switch ? How would you even know that Search Engine 26 is quite a bit better for most of your queries ?
Do you genuinely think most people are performing lengthy evaluations before they switch default back to google ? so how do they know Bing or whatever isn't better for them ? The answer is that they don't. And it doesn't matter because unless something blows it out of the water and gets people talking then people will not switch.
Familiarity and Trust is basically branding and that's a huge reason people stay on platforms even when there are no network effects.