First, let me preface this by stating that this is a newly forming opinion based on not having really thought about this issue before. It is also based on reading a lot about TTRPG. I am perfectly willing to be "wrong" or out-voted or whatever. This is not a hill I want to die on. However, since you asked, I'll explain myself a little more ...
The base idea is that this is an adventuring game that is not meant to depict or model real life, but rather encourage players to get out into the adventure. As such, that means adventuring should be rewarded and not-adventuring should be discouraged.
As for all of the practice, here's how I'd explain it: Downtime practice provides two benefits:
1) This is what your character does to make sure he doesn't lose the skill they have already gained. Having the ability to efficiently stab things with your sword is a hard thing, and the practice makes sure you don't lose what you have already gained.
2) This is where your character actually gains the improvement based on the practical experience they have gained. I.e. the practice is where they are spending those 8 XP to gain a base proficiency or weapon mastery.
So, all that practice is very important and very useful for the character. It just doesn't have an obvious mechanical benefit because the XP is only earned while adventuring.
As for the "soft" skills, I'd never make a character roll to cook a meal or play an instrument or speak a language. Now, if they are trying to cook a very fancy meal for in-game purposes, or play an instrument as a performance in front of the king, or speak to the Elven emissary in Elvish, then, yes, you have to make a roll. But those roles will rely more on your Education, Charisma, or whatever, than they will on your soft skill.
And I am not 100% on board with being able to even add a new "background". Remember, it took your character their entire life to gain that background. I don't think someone should be able to duplicate that in their spare time between adventures.