Your position baffles me. Do you dispute the evidence that there once were creatures on this planet that fit into the gap between humans and chimpanzees? For example, do you dispute the existence or veracity of the "Lucy" skeleton, which has characteristics intermediate between humans and chimpanzees?
If you do dispute this, perhaps we could start a discussion about the nature of this evidence and why we think it supports evolution: there are many knowledgeable people here who could give you a very thorough explanation, if you'd like one. Or, you could read about it here, for starters.
If you do not dispute this, then I have to ask, are you only questioning why they should be extinct? I am curious to know why you think a living organism would fill an evolutionary "gap" better than an extinct one.