The problem is file size. When you make an animated gif, you have to duplicate each frame that will change. The smoother the animation/transition, the more frames you need. The new slight sig size limit increase makes doing animations easier, but they are best limited to things such as flashing eyes, gems, light beams, etc. where you don't need a whole lot of different frames to create the effect.
If you recall Feyre's "happy fun" sig, with the stick figure drawings, that was super cute but as limited as it was, I think he barely got it under the old sig size limit, but he kept his canvas area pretty small so it worked. Same on the one he made for someone else with the giant foot that stomps the stick figure.
-Skylark