I think it has something to do with Universal's lack of legacy of watchable cartoon shorts, shows and characters, comic books, and stuff like that when compared to Warner Bros. and Disney. There were plenty of instances where Universal could have had a chance to acquire popular assets in order to grow its company to be as competitive.
1) Hanna-Barbera. Had Universal simply acquired the famed company as originally intended, cartoons like Johnny Bravo, Ed, Edd N Eddy, and Dexter Lab would belong to Universal instead of Warner Bros. USA Network (which Universal acquired in the mid-1990s) had a cartoon block called "Cartoon Express". I could see Universal spinning this block as its own cartoon-like 24 hour network. Adult Swim will inevitably exists, that's for sure, and Universal would be in the business of producing adult-animated shows/movies. WB IMO would be left without a 24 hour Cartoon programming network like 20th Century Fox (now absorbed into and owned by Disney) and Sony.
2) Marvel Entertainment. OK, this one that Universal didn't really offer a deal, but what if they did instead. It would have elevated Universal to be as competitive to Warner Bros. instead of Disney.
3) Funimation. I don't know about that one, but Universal was going to seek it as well.
4) 21st Century Fox. Yes, it's not much when compared to the other first two (and probably the third), but at least it will give Universal a valuable library such as Fox adult-animated sitcoms and X-Men movies. We'll probably have a Deadpool adult animated series by now too.
If Universal has all of these (maybe except #3 or #4, or both), they would be indisputable and competitive to Warner Bros. and Disney and would no doubt expand their reach more influentially. Documentaries about Universal parks would have been made on the service by now. Unfortunately, Universal currently have none of these options listed here, and people aren't as excited about Universal products when compared to Warner Bros. and Disney.
Universal owns way more animated properties right than you know. The difference is they let others distribute (Universal produces/own rights to the anime Seven Deadly Sins however its a Netflix Original) Just because they don't tote them out like WB and Disney, their library of property rights is more vast than even you would believe.
Japanese Animation
NBCUniversal Entertainment Japan - Companies - MyAnimeList.net
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Dreamworks Classic
DreamWorks Classics
DreamWorks Classics (formerly Classic Media) is an American entertainment company owned by DreamWorks Animation. It was founded as Classic Media in 2000 by Eric Ellenbogen and John Engelman. The studio's library consists of acquired intellectual property catalogs and character brands as well as...
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Dreamworks Animation Television
DreamWorks Animation Television - Wikipedia
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Dreamworks Animation:
List of DreamWorks Animation productions - Wikipedia
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Universal Animation Studio
Universal Animation Studios - Wikipedia
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Universal is competitive enough on their own. Thats the same reason they didn't buy IDW or Image comics when they had the chance.