Originally Posted by JFarrell71
Because in a P&P game you can anticipate rolls and force rolls. In a computer game, you cannot.
For example, say I'm about to talk to someone and I want to know if they're lying. So in a P&P game, before I approach them for that conversation, I cast a spell. Detect Truth or whatever it's called (there is such a spell, I'm just not looking up the exact name of it). When I then speak to them and they answer, the GM is going to be obligated to take my spell into account. Same principle applies if I want to persuade someone, and I cast something (Guidance, Luck, etc) to improve my roll to do so. I know beforehand that I'm going to use it, and by deciding to do so and telling the GM that's what I'm doing, I create a situation in which the modified persuade roll is allowed.
In a computer game, I don't know if the game is going to allow me to persuade someone until I get into that conversation and see or don't see that option. I don't know if the game is going to take my Detect Truth spell into account. A game cannot account for all possible contigencies; it presents you with a set of options that the developers foresaw, and you choose one.
It would be terrible game design to force the player to cast such spells preemptively just in case they're about to be useful and then waste them if they aren't.
So in order to capture the spirit of the P&P rules as in scenario #1 above, you do what Larian has done with the active roll system. Makes absolute sense to me.