Because it's technically no one else's business regardless of their reasons for wanting to look. I even sometimes get paranoid that MG staff take liberties by being able to look at any old private racks they like "just cuz".
It's not that I'm hiding anything in most cases (no pun intended), though I have uploaded some non-existent, hidden "concept" modules on here which may or may not ever be realized. And I'm also not here to impress people. I use the grid for planning my racks, both real and theoretical, sometimes in multiple, messy iterations. Why does anyone need to see that? More practically, why might I want to tip people off to what unobtanioum modules I'm scoping out at any given moment? >:3
If I want opinions, I'll ask. I'm not spending 6 hours obsessively moving squares around for any of you, though!