Re: Why no tsuba?
A way to rephrase the "because this is the way the founder did it" answer is that the founder trained in a way that didn't requite a tsuba. This training was formalised and put down as a methodology by Saito Morihiro sensei as what is called the Iwama style which maintains this feature of bukiwaza.
Other teachers derive their sword training from different sources which explains the variation in approaches. The litigious societies some of us live in are also a contributing factor.