Something I've noticed...
I have two theories:
1. People just rambling on about their lives have left Blogger in favor of some other blogging space. I think, and this might sound a little mean, but it's not intended to be, that many of the bloggers with the trailing-off kind of titles were teenagers, and maybe now that more of the social networking sites also include blogging, they've left blogger for those sites. Maybe different blogging sites attract different kinds of bloggers, or people who blog for different purposes.
2. Maybe blogging is maturing as a writing genre. I think most people are more likely to explore a random blog with an actual title than they are to click on a random blog with no real title. This could drive an evolution towards creating a distinct identity for one's blog by giving it a memorable title.