GNOME isn't a toolkit, it's a full desktop environment. The toolkit is GTK+.
And yeah it is heavier than Motif. It does a lot more with it, though. Whether you think those things are valuable or not presumably depends on what software you use and your own sense of aesthetics.
Also when GTK+ was created, Motif was proprietary. There was Lesstif, but if I recall correctly that wasn't all that good, so there was a good incentive to develop a Free Software GUI toolkit.
And yeah it is heavier than Motif. It does a lot more with it, though. Whether you think those things are valuable or not presumably depends on what software you use and your own sense of aesthetics.
Also when GTK+ was created, Motif was proprietary. There was Lesstif, but if I recall correctly that wasn't all that good, so there was a good incentive to develop a Free Software GUI toolkit.