Yesterday I went through my enormous "books to read" pile and realized that more than half of them I did not choose. Publishers send copies hoping I will blurb them. Authors send copies hoping I will recommend them when I speak to large conventions of teachers. I keep them because their topics interest me, or should, and I intend to read them tomorrow.
Of course, tomorrow never comes, at least not to my book pile. Time does march on, however, and soon it's too late to blurb them anyway.
How do "real" blurbers and reviewers keep up? Well, some cheat. They blurb books they have not read, not even skimmed, only looked at. Or, as we used to say in grad school, discussing a source glibly, "I haven't read it personally, but ...," and we proceeded to invoke or dismiss it, hopefully to good effect. (This is called "socialization into the profession.")
I cannot bring myself to blurb a book I haven't read, so I hardly ever blurb anything. But my heart is in the right place. I try to read what authors and publishers send me. I just fall behind.