In our dojo, the very first thing you learn are the basic breakfalls, especially ushiro ukemi, yoko ukemi and zenpou kaiten ukemi. For us it's a safety factor that also forms part of the raw basics of learning Aikido (like tai sabaki drills and reaction/timing drills).
If you can't protect yourself while falling it can negatively affect the practice of both persons involved in kata practice. At the level of randori (which starts very soon after a few beginner classes), not knowing Ukemi is asking for an injury, maybe a serious one. So, safety first, this is why we teach ukemi first.