Okay, am I crazy or is carry-on luggage getting smaller?

I have a carry-on that I want to replace because it is old (gross?) and the zipper is not working so well. It is the size that everybody used to have but now all the carry-ons are smaller. I want to buy a new one that is the same size but it is harder to find now. Why? Don’t people want to carry-on the largest suitcase they can?

What is going on here?  Why are people using tiny suitcases now?

Travelers explain!