With small suggestion, the only real effect is that people vote for things in the first part of the list and don't bother reading more.
The real effect is that small suggestions disappear when completed or rejected, and they do so fast, keeping the list in flux and bringing newer suggestions to the top.
Besides, people do find small suggestions to vote on: I've kept track of a few suggestions and I've seen them climb slowly, vote by vote from zero to nearing the top 20. Even as we speak there are small, new items being added and voted on. While the big ones clutter the top of the list for years.
Someone argued for opening the list to more players. Enforcing small suggestions only would have the exact opposite effect - making the eternal voting more elitist.
Does not happen, people find the small ones. Especially when the big ones aren't there to suck up all votes forever.
And that's not to mention how would you handle it technically? Any idea for a real implementation of suggestion limits? Who would judge what is small and what is large? How would you set the rules? Where would the dividing line between small and large be? Even if you managed to answer all of this, you'd find out everyone feels it differently and that people keep posting what you consider as a "large" suggestion. Who would moderate it then? Toady wouldn't.
Just have another list with the big themes/arcs. (Items only added by mods, limited number of items). People who want to urge Toady to work on a big theme can do so there. The ESV we have now can stay as it is with a big note that collections will be ignored and you can vote for that in the other list.
The two would stay because people who voted for them have already stopped caring and don't bother to come back and relocate their votes Really, the list needs periodical resets even if it is just for deleting "dead" votes. I personally am for periodical wiping of the suggestions too, to delete "dead" or "abandoned" suggestions.
Not all people have always enough time to check the ESV... Let votes be wiped when the suggestions are implemented, that'll keep the list up-to-date. Temporarily absent players are players too.