Of all the handgun companies, Ruger had, and probably still has, more experience in fabricating Titanium then any other - not because they built guns out of the stuff, but because of the many other products they made out of this material.
And Bill Ruger Sr. decided that Titanium handguns represented a direction he didn't want to go. He foresaw problems that he didn't want to get into.
The company's culture is such that they don't feel the need to match every competitor's products, model by model. They make what they see as being right for what they do. This of course is going to make some folks unhappy.
Ruger is also one of the few companies left that doesn't have substantial debt - which is to say they don't run on borrowed money. They expand when the feel ready to do so, and can do it out of their own pocket.
They are also not completely focused on handguns because they build rifles and shotguns as well.
Both the GP-100 and SP-101 were designed to do a certain thing, and do it well. I think it’s unlikely we’ll see any radical changes or expansion of material options in either model. But I could be wrong… Bill Sr. is no longer around. Those that knew him will understand what I’m saying.