In those cases where forking has been a solution to a problem that doesn't exist, those forks normally fail to gain any traction. Nothing is lost except for a developer or two from the original project. If those developers have made an unsuccessful fork, it probably means they disrupting the original project anyway.

There are many reasons why someone may fork a project. Sometimes it's absolutely necessary. It's part and parcel of open source software development. There are countless cases where forks have superseded their original project and other cases where they have provided a credible alternative: LibreOffice, OpenBSD, LibreELEC, MariaDB, CyanogenMod, Replicant, WebKit, Jenkins, Devuan, LibreSSL...

Some call it fragmentation, others call it progress. I hope you're not still using OpenOffice, MySQL, XFree86, etc.

We're all here on this forum because we're interested in an alternative to the world of iOS and Android. That in itself is fragmentation. Those who don't don't like fragmentation tend to stick with iOS or Android.

EDIT: Just to be clear, my above rant relates to nthn's comment, in particular, the 99% part. I don't agree with Jolla's decision to create a new app ecosystem by introducing the proprietary Silica Components meaning apps for Sailfish will not run anywhere else. That is a great example of bad fragmentation and is definitely not progress.