I wish the game would focus on being for medcore players more.

[Absurdity]

They don't do it as much seemly because of a belief players desire consistency in fights, and you can notice how the most random mechanics are almost always in casual content barring a few exceptions, a good example of this is my lovely queen, Honey B. Lovely, in M2N, during Honey B. Live, the slow-moving hearts have a very erratic, difficult to predict pattern to them, I am sure it's not completely random but it might as well be, and there are tons of AoEs all over the place on top, then in M2S, during the same segment, the hearts have a ridiculously predictable, easy to dodge pattern, and the AoEs are replaced with tower soaks that anyone can take so long as it is in their heart budget(on Normal tower soaks do happen, but not until the 2nd Honey B. Live), meaning they throw the more punishing, but nonetheless more predictable version of the mechanic at you right away, there is a clear flow here that the harder the content is meant to be, the more predictable they want to make it, with a few variants, 2 to 4, of the same mechanic at most. and which variant you get being the random element.

If someone dies in a normal mode it usually doesn't matter, you just get them back up and continue, so randomness isn't an issue.

But because pretty much everything in savage kills you instantly if you mess up, which then leads to cascading deaths or an entire party wipe, the punishment for even a single player messing up is significantly harsher. Which doesn't lend itself very well to random mechanics.
You already need to memorize 8+ minutes of quick and precise execution to not reset the entire fight constantly, making those mechanics erratic and random as well will quickly lead to frustration.

It is basically a problem they have created for themselves, by designing savage mechanics in the way they have since late ShB.