The inability of the GIMP developers to work with others to incorporate needed features was the primary reason.
Look at the difference between how different open-source projects operate. Some foster collaboration and encourage outside contributions, e.g. Linux. Others are completely insular and barely tolerate it. The GIMP maintainers fall into the latter category. Unless you're part of the inner clique, you won't get anything merged.
It's kind of sad that the Cinepaint people got several paid staff to lift the GIMP functionality to the point it had very high-profile commercial use with some really useful features, and yet the GIMP developers were too stubborn to acknowledge this effort and work with them to get the functionality into the GIMP core.
Sadly, this is not unique to the GIMP. I, and other commercial developers, had exactly the same experience with GTK+ and GNOME libraries. The developers wanted to hack on their pet thing, ignore outside contributions, and this is simply not compatible with commercial timelines and realities. But it can be, and it can work very well, for projects which are willing to engage with outside work. It can work out to be very mutually beneficial with some give and take on both sides. I was on the GIMP mailing lists at the time and followed this saga for years. It's a crying shame it was deliberately ignored.
Look at the difference between how different open-source projects operate. Some foster collaboration and encourage outside contributions, e.g. Linux. Others are completely insular and barely tolerate it. The GIMP maintainers fall into the latter category. Unless you're part of the inner clique, you won't get anything merged.
It's kind of sad that the Cinepaint people got several paid staff to lift the GIMP functionality to the point it had very high-profile commercial use with some really useful features, and yet the GIMP developers were too stubborn to acknowledge this effort and work with them to get the functionality into the GIMP core.
Sadly, this is not unique to the GIMP. I, and other commercial developers, had exactly the same experience with GTK+ and GNOME libraries. The developers wanted to hack on their pet thing, ignore outside contributions, and this is simply not compatible with commercial timelines and realities. But it can be, and it can work very well, for projects which are willing to engage with outside work. It can work out to be very mutually beneficial with some give and take on both sides. I was on the GIMP mailing lists at the time and followed this saga for years. It's a crying shame it was deliberately ignored.