Some players would rather experience the whole game (what does this spell do? Is it cool?, etc.), instead of just focusing on one type of build and/or resorting to some type of guide or wiki to minmax their experience. I think RPG developers should always consider allowing players to respec (re-allocate their choices) mid-game, so they can always try out different builds without having to start from scratch.
It is indeed fun to explore the full space of the game via a diversity of strategies for each class, but the point is that it will be optimal to explore them in distinct playthroughs. Runs of Slay the Spire are fairly short and it is designed for replayability, and it's also specifically balanced around the notion of the player exploiting synergies, so it will disfavor an unfocused deck.
In my opinion RPG developers should not only NOT do that, they should even do the opposite and hide more content behind exclusive choices of player character traits. I believe that most video game RPGs focus far too much on making these choices irrelevant and allowing to change them on a whim just perpetuates that.
Every beginner Diablo 2 player puts one point into every skill, instead of focusing on 1-3 main skills that should get 20 points and 1-5 points into secondary skills/"one point wonders".
Slay the Spire addresses this via the randomness of which cards are offered, which means that you have to design a deck without being remotely guaranteed to receive the cards necessary for whatever meta deck you have in mind. Unlike Diablo it's also exclusively a single player game, so there's less pressure to compete and more freedom to just have fun.