UIC sample suplies several convenient codecs that make the IPP library very easy to use. But why there's no gif decoder contained in it?
In terms of being able to pick up UIC and start using it as an image processing library it's understandable that the lack of more formats may seem like a gap. However, the main reason why there is no gif decoder (and why support for some image formats was moved to legacy in IPP 7.1) is that the samples are there to showcase how the primitives might be used in an application. The UIC sample is primarily there to illustrate JPEG optimization, not GIF. UIC is just a starting point, and not intended as a product-ready image processing solution. Fortunately there are many very good turnkey image codec/processing libraries if that's what you need.