Back in 2013 when Event Logging was first added to ULS, ULS was used in very few contexts—interlanguage area (for settings, not for Compact Language Links), personal bar, target language selection in Translate, and hardly anything else. Now in 2017, it is used all over the place: Wikidata, Upload Wizard, Compact Language Links, and other places.
Different contexts have different needs for logging. Last week when I was analyzing the data about failed language name searches (see T178996), I realized that many valid languages are not found because in some contexts they are not supposed to be found. For example in Compact Language Links, when an article is not available in that language. It may still be useful to log this failed search, but it will have to be analyzed differently. In Translate, differentiating Traditional and Simplified Chinese is useful, but not in Compact Language Links. And so on.
So this must be fixed by updating the schemas and the logging code. This will open up curious new possibilities, for example being able to learn for versions of which articles are people searching in their language and failing to find.