1. Gallery as a tool to teach people socionics. When you add so many IEIs to your gallery and so few SLIs people may think the former type is very common in society and the latter very rare. They won't be aware of your way of creating it and can make wrong conclusions about socionics. Also, more examples of a type mean more information to learn about a type. While 12 SLIs is enough to give an idea what this type is about, it's certainly not enough to understand this type in depth (differences between subtypes, characteristic behaviors in different gender/age/occupation etc.). If you decide to look at possible SLIs and type another 12 of them you would get two times more examples of this type, two times more info, while typing another IEIs that you already have a lot of would be much less significant, a waste of time in comparison.
2. Gallery as a data source for research. There are many different ways in which a well-made list of typed people may be used for analysis, it's a promising direction to help improve socionics (looking for correlations of traits, AI facial recognition etc). I don't think I have to explain why it's important to have many examples of all types to make it work. I'm working on the consensus list for this reason and I need quality typings of all types so the quality of what you do may also influence socionics development in the future in some way.
3. Gallery as a way to make money. You're knowledgeable in socionics, so you can try to find ways to profit from it, Gulenko is quite successful with his typing services, you may find your own niche too. In this case a well-made gallery with many examples of all types would attract more people to you as a professional, improve your reputation.
4. Gallery as a self-development tool. Maybe you're doing it mostly for yourself and you share the gallery because it's not much work to do and someone using it is a nice side effect. When you try to type people you gain experience in socionics, looking at a whole list of previously typed people is great to spot some traits typical to a type that you could miss just by typing someone and forgetting about it. IEIs are more interesting to you, you watch more examples of them and learn more about them, your understanding of this type is much better than your understanding of SLIs because of it. Maybe it's ok for finding compatible friends (why IEI instead of ESE then though...) but in real life situations we interact with all types and equal knowledge about them helps to have good relations with people in general. You can say SLIs are not interesting and avoid them but maybe one day an SLI client shows up in your company interested in your product, you fail to encourage him to purchase it because you don't have enough experience with this type.