david_prentice:
Anyway, your ESP32 will be able to animate uncompressed bitmaps. The biggest advantage of GIF is that all the frames are stored in a single file.David.
Yes, and the file size. The actual welcome screen on the finished product will very probably not be 15 seconds long and contain 177 images, but it's just more handy to have it in a small compact file. Some 700 KB for the animation above, but as 128x160 x 177 frames as 8-bit BMP, we're looking at 3.5 MB if I'm not mistaken.
I've tried to find a GIF decoding library online that could be ported to the Arduino, but didn't manage to find anything so far. What you do see on web forums is people asking around if somebody has a good GIF library... 
I would love to write some code myself to decode and display GIF images. But my programming skills just aren't up to that.