We as humans do not know what it's like to not have a personality so we can't relate to things that don't and thus treat them as if they have personalities. Quite simple.
People have sympathetic reactions to machines already. I know other people who cajole, threaten and beg their cars to work. Thanking a machine doesn't make logical sense, but it's not really too abnormal.
Well, if my CD Player look my size and and looked at me and said "CD Ejected", I probably would thank it too, lest it goes haywire and beats my bone and flesh butt! It wouldn't be the only pointless thing I have ever done. lol