Probably because the differentiation between "macro-evolution" ("speciation") and "micro-evolution" is an ID foil. *ALL* evolution is microevolution. There's nowhere in evolutionary theory that says a frog must give birth to a mouse for evolution to occur. Micro-evolutionary changes are sufficient to explain speciation over a long enough time frame.

One of the recurring problems in these kinds of discussion is the definition of speciation. If you nail down an ID'er with evidence of speciation, they change the definition ("Oh, well, it's still a bacterium, isn't it?" ) and start talking about an amorphous concept called "kinds". Then you show the feathered dinosaur fossils, and they yell "hoax" (in spite of the fact that there have been many more species of feathered dinos than archeopteryx discovered), and when that doesn't pan out, they say it's not really a transitional species, it's a distinct, god-created animal that is now extinct. This is clearly the avoidance behavior we all sometimes engage in, designed to protect a comfortable delusion.

You can't 'win' this kind of argument. The BEST we can hope for is that it will fall 'out of fashion' over time.