You are right in your logic: if everything started from nothing, then everything would be compulsory. There is a lot to be said about that in relation to life. If I start from nothing with no help, then I am forced to work hard all my life. That hard work becomes compulsory. I have to do everything that I have to do in order to survive. If I start from nothing, then everything in my life is compulsory, and that is a sad state of affairs.
The universe couldn't have started that way, and we can be secure in that knowledge by the fact that nothing is an idea in two parts. The parts are no and thing: no thing. A two part idea could be a complex idea. A simpler idea than "everything started from nothing" is that everything started from a primal Thing. Thing is a one-part idea. Rather than a natural state of nothing, as we tend to think, the most natural state is the state of being "Thing".
This becomes important when you define the nature of a mathematical point, since physics is sure everything started from one mathematical point. Is a mathematical point a thing that has size, or is it sizeless? If it is sizeless, then it is nothing. The idea that everything started from nothing, as you began to see, has problems.
The solution is that nothing is a two-part idea. One part of the idea is "Thing". Everything started from "Thing".
Physics says everything started from a non-dimensional point, which is a point-particle that did not have any size. But the Bible says that everything started from an abysmally large sea. This sea would have contained all the raw matter in the universe. It exploded, and the explosion created many points of matter from this huge sea of matter, as it exploded. These points of matter organized into the universe we know.
Physics has a problem. It can't unite the quantum world with the everyday world. String theory says it can unite the two. String theory starts with the concept that all points have size, all points are strings. String theory says points are something that actually exist as strings, rather than being dimensionless and sizeless.
Did everything start from nothing? Everything did start from one point, as physics says, but the point was a string. A string can have any size. It can be abysmally large. It is a Thing. Everything started from Thing.
Now we have an interesting dilemma. If points have size, if points are things, if everything is constructed from points, then you have to stack string points in a specific way.
Here is a plane made of strings. It only has three directions. If you construct a plane from strings, which have a size, length, then you get a plane that contains only three directions. To get from A to B on this plane, as you can see, you have to zigzag along two of the three "dimensions" of this string plane. If the points didn't have size, you could go in any direction when going from point to point; but if they have size you now have a built-in structure, and that gives this plane 5 dimensions, which are the two dimensions of a plane, plus the three underlying directions, which are all the directions that can exist on this plane of string points.
In 3D space using this logic, you get six underlying directions, which become six extra dimensions. When you add the four dimesions of space and time, string theory spacetime has ten dimensions.
But underlying string theory is the idea you realized: only nothing can start from nothing. Everything had to start from a thing that has at least one dimension, it had some kind of size, it was a Thing. We call it a string.
So, when talking about string theory, string theory is the argument, "Did everything start from nothing? Or did there always have to be something that existed, if only as one large point of raw formless matter, like the abysmal sea in the beginning of the Bible?" Did everything start from a string? A string is a thing, not nothing.