that and it takes a while to see them, i have had the smaller ramshorns in my tank for many weeks now, have seen lots of egg sacks come and go (only have tetras that i dont think eat baby snails) and just recently have started to see a tiny white spot here and there, i have to use a magnafier to make out that it's a baby snail.
lol my roommate caught me the other day with the magnifier searching the tank for more (i love snails and have been waiting patiently to see babies) and made fun of me.
that and if you do any 50% or more water changes, move gravel or plant some plants i think it might have an impact on it. i recently did a 75% water change to move my tank and add rocks and moved plants around and such, i moved my bigger snails so they wouldnt get crushed or anything but havent seen any white dots since