I think if you don't have 10 spaces for eidolons and weapons each, then it will lower the amount you can draw. A lot of times though it will just do it randomly if you've already drew a few times. The only fix I've found is to click My Page and go back to the gacha screen again. It's one of my many minor annoyances with this game.
I don't think the 100k gem limit thing is true though, since I used 120k yesterday.. just had to keep refreshing and going back to the gacha screen over and over while selling eidolons/weapons to keep space.