How is losing an ability part of evolution?

Alright, so it's believed the appendix and one point helped in our disgestion of dietary fibers, and we could consume grass/bark/plants like heribovores. So how is losing that ability evolutionary?

One needs to realize that evolution is not a conscious choice towards a "better" organism.  It is simply the combination of a  constantly changing envyronment and a constantly changing genetic makeup shifting.  when you ask why something is or why something isn't, there isnt always an "It's better that way" answer.  sometimes, and indeed with more recent genetic mutations, oftentimes, the answer is simply chance.