Sharan here with my two sense.
Personally, I agree that writer's block is an invention. You never hear of painter's block or choreographer's block, but those involve the same degree of creativity. People in any line of work sometimes find themselves unable to decide what to do next. So why did this odd ailment get stuck to writers?
I have two possiblities. The first, sadly, is that it was invented by an author who had already drunk away the first part of the advance and needed an excuse to extend the deadline or wheedle a bit more cash from publishers and friends. The second thought is almost as sad. It may have been thought up by a writer who suddenly discovered that she had nothing to say. It's not something any of us would care to admit.
Once upon a time, and I do mean a long time ago, I was working on my third book and was really stuck. I just couldn't figure out what was going to happen next although I could see the conclusion far away like the point of a mountain top from the desert. That year I went to the Santa Barbara writers conference where I met people who are still good friends and the agent I've been with for thirty years. I didn't mention my problem with the book but I went to some late night readings by others needing advice. After a long passage, someone said to the writer, "It's good work, but it doesn't belong in the story."
I had written a chapter I was in love with but it didn't belong in that book (I used it elsewhere later). Once I'd admitted this and tossed out the pages, the book started moving again. Ever since then, when I come up against a wall, I ask myself, "Does this thing blocking up my story really belong there?" Often, like a drain full of peanut butter, it doesn't.
I still don't believe in real writer's block, but sometimes one does need a metaphorical plunger to get rid of a clog and let the work flow smoothly once again.