We can't just add more and more features that double or triple your Skill Shard intake per week; we'd very quickly reach a point where Skill Shard rewards are meaningless. Like, if you got 12 Skill Shards a month base, and we added 3 features that increased you Skill Shard intake by even 50%, the first feature would make it so you gain 18 per month, the next would make you gain 27 per month, and the third would make it so you gain 40 per month. The numbers become silly if you consider percent increases based on previous yields instead of absolute value improvements, especially when most (non-Eddie) characters take 6-10 Skill Shards to max.
Even setting aside the raw amount of Skill Shards earned, if you got 50 Rare Souls, what do you expect you'll get out of them? What is the best you'd expect to get out of them?
For a lot of long term players, more characters is purely a matter of raw essence, since certain kinds of souls literally cannot give them new characters (again, situational exceptions like the new addition of Valkyries can occur). If the goal is more Skill Shards, getting 2 Skill Shards directly is more Skill Shards than the average expectation of any other result when considering how close other results will get you to another high-tier sacrifice and how much progress you'll make towards a Vortex.
Legendary Souls are a different consideration, but they're the best chance to get natural 5 star characters, and they can get 5 stars of any class, so they're still the ultimate prize for finishing a collection and getting the rarest new characters we add.