Your assertion that biologists would make such an assertion is unproven.
Your assertion that there is no giraffe with shorter necks is false, as okapi is of the same order.
I concede the short giraffe. As it was a hastey example, it is hardly a pivotal matter. Some giraffe got taller, some didn't, both survived. Sort of negates the supposed advantages of either. See the total supposition works both ways, and is just as scientific.
You are truly stating that biologists don't make assertions about "why" animals developed certain traits? I guess you've never read a textbook or watched a nature documentary. Again, obstinance raises its ugly head.
If only academia were half as scientific as you claim...