Why do files with longer names have a smaller hitbox on the desktop?
Solution 1:
In my experience, Windows selects icons if you include a certain share of them in the selection box. Icons with longer titles are higher, as they extend down because of the linebreaks in their title. You therefore need to select more of them to hit the treshold.
As for why this was implemented I can only guess that it is the same algorithm that governs all icon selection, and is a useful approach that works for all icon sizes (try [Ctrl]+Mouse Wheel to resize icons and preview images).