Does the average Christian layperson really care about all of these philosophical arguments for the existence of God? Why?

I would say that the average layperson does not give a rip about the philosophical arguments for the existence of God. I would further posit that most of them do not even know these arguments. I would say that for many of them, the existence of God is explained in their personal experience and relationship with him. That, for many, is all the evidence that they need. The problem is that in a lot of circles of unbelief, this is not deemed a measurable quantity to be analyzed. With that said, these philosophical arguments should be a buttress for those things that we already experience as we grow and walk with Jesus, living in us. Evidence to back up the experience is an even greater tool in sharing the love and knowledge of Christ.