First, someone proposed blocking all-caps questions. This was declined. The decliner seemed to feel that the problem was too rare to bother with.
Well, all-lowercase questions are 50 times more common than all-caps questions. Stack Overflow gets only about 100 all-uppercase questions per year; see here. Yet it gets about 5,000 all-lowercase questions per year; see here. (These statistics are for Stack Overflow only; the rest of our network wasn't considered.)
All-lowercase questions are often of poor quality. Let's block them.
Note: If you disagree with my idea, it would be helpful if you could please tell me why you disagree.
P.S. This idea is modified and adapted from an older idea by stack exchange user Gilles. My dear sir Gilles, I thank you.