Easier for people not used to dice systems to understand. It’s immediate and obvious, most non dnd players can grasp it at a glance.
I repeat my point: you could have the option of toggling it off. Both types of people would be happy, then - those who don’t like percentages and those who do.
And I repeat mine... If someone is interested in playing D&D at the table, as BG3 will undoubtedly foster for many, showing the target d20 DC in the combat tooltip, which is essentially the same exact thing as what the dialogue UI is doing, will (most likely) ease the pain of understanding how attack rolls work for a tabletop game. Showing percentage to hit in combat and a target d20 DC in dialogue is inconsistent and more confusing for people looking to play at the table.
You seem confused about what the game actually tells and shows you.
You don't know the DC of a dialog check before you choose it. That's why you're only told what your flat bonus to the d20 roll will be and if you have advantage or disadvantage. In combat you know everything you need to calculate the percentage success rate: Targets AC / saving throws, your attack roll mod / spell save DC, whether you / the target have advantage / disadvantage.
If you want to know what your attack roll or spell save DC is, just look at your character sheet / inventory or whatever. The green/red chevrons tell you if you or the target have advantage/disadvantage. Everything you want is already available?
I'm really not confused about it. We're talking about the tooltip, not the character sheet, chat log, combat log, or anything else. And the idea here is to foster an experience that eases the burden of people who are interested in a tabletop experience to transition into the scene.
Let me paint a picture for you.
Mikey has been playing BG3 for about 2 days. Mikey sees an arbitrary percent to hit and wants to know how that percentage is calculated, because he wants to increase his chance (like any normal player would want to!)
Sometimes Mikey sees advantage (from high ground, being hidden/invisible, etc.) and that obviously bumps the hit percentage. Great! But there are underlying mechanics going on that should be elucidated in the tooltip, much like in the dialogue UI, that are decided by a d20 roll and the commensurate DC. Understanding these mechanics is fundamental to being able to play a tabletop game of D&D 5e.
That's my argument. Players at a tabletop game aren't going to know their "hit chance". They're going to have to understand the underlying mechanics to make informed decisions about combat. So Mikey can say, "I get +3 to hit. I think that kobold has a 14 AC, so I need to roll an 11 to hit." These numbers shouldn't be buried beneath inspection layers of the UI. They should be shown in the tooltip for combat, JUST like they are shown in the dialogue UI.