I’m on the first episode of The Good Place and I am just wondering if they've given any sort of reason for this at any time in-world/series so far.
It's very hard to answer this question without significant spoilers.
About the only thing I can say in the open, is that what you are seeing in terms of points isn't really the whole story; there are aspects that you don't understand which will cause it to all make sense. I'll explain more in the spoiler section below, but I really wouldn't recommend looking at it if you are only on the first episode -- all WILL be explained.
The assignment of points (as explained) is meaningless; things are not what they seem.
The whole dilemma, as presented at the point you are watching, is that our Heroine has found her self erroneously placed in the Good Place, and is trying to figure out how to not end up being tossed into the Bad Place when the mistake is discovered. She knows a mistake must have been made (and that she should own up to it), but she's hoping to improve enough to earn her right to stay in the Good Place by the time it comes to light.
Actually, she's exactly where she's supposed to be.. She just doesn't understand the full picture. Yet.
I would strongly recommend you NOT read the next spoiler. It will give away a MAJOR plot point.
She's actually in the Bad place, and all but a few of her fellow 'Good Place' residents are demons. The whole place is an experiment in setting them up to torture themselves and each other with minimal involvement from the demons. The points and everything else mean nothing -- they are all just to provide verisimilitude, and keep things confusing so as to make it harder for them to catch on to what's really going on.
There really is a point system that determines their place in the afterlife (in this case, relegating them to the Bad Place), but they are having things explained to them by an unreliable narrator, in effect, so what he says about any individual assignment of points is not necessarily anything to do with how they are/were really assigned (were, since assignment at end-of-life is supposed to be the end of it - but more on that in the next season...) Eating a sandwich MIGHT give you good points for some reason (since he does stick to a lot of the truth, only lying when useful), but given the unreliable nature of the narrator, we have no way to know.
Every action is a complicated mixture of side effects and intentional consequences.
For example, by eating this sandwich, are you preventing someone else from having it -- perhaps someone who might need it more than you do? By making/buying the sandwich, are you contributing to the exploitation of the workers who labored to produce its ingredients? And what about the environmental impact of raising the meat that went into it?
But on the other hand, are you generating a positive economic effect, by giving employment to the people who sold you the sandwich or its ingredients? And what if someone else made that sandwich for you, as an act of benevolence? Is appreciating their kindness by eating the sandwich an inherently good act in itself?
As you continue to watch the show, this theme of the moral calculus behind seemingly simple decisions will be expounded on periodically through the character of Chidi, who is an expert on moral philosophy. I think his explanations of things will help you see how the show approaches ideas like this.
This is largely addressed in later episodes. Points are gained and lost based on the net utility that the action creates, just like winning and losing points in a video game. Buying a sandwich from a local vendor, for example, is likely to have a greater net effect than buying one from a large corporation, given that the show seems to subscribe to a general 'small companies good, big companies bad' mentality.
On the subject of sandwiches, Eleanor gives at least one a specific instance where buying a certain kind of sandwich is associated with being a homophobe. Whether that's true or not, making that buying decision is very likely to result in a strong net positive or net negative score.
Eleanor: Yeah, there are booby traps everywhere. Like, there's this chicken sandwich that if you eat it, it means you hate gay people.