Also, futureproofing.
Yeah, that's one I don't see really. One Titan is what, £900? So by going for one rather than three, you are saving £1800.
Pretty sure you can build a PC in a few years time for that which will spank these Titans all day long. And one Titan X would probably run most games fairly well at 4k.
I think in this chap's situation, the answer to the question is "because I can and I enjoy it".
Fair play i say.