I disagree. I think maths are intrinsically complex. Some results may have intuitive geometric interpretations but if you want to understand the whole edifice, there's no shortcut, you have to absorb tons of theories.
Take probability theory and statistics, you can always see it a set of recipes, but if you really want to make sense of it, you need to study maths for a few years.
So you can compare current mathematics to be like a certain programming language. Let's say it's like FORTRAN. There might be C++ for the same concepts, there might be Python, Smalltalk, Prolog or Haskell for the same concepts, but everything you read is in FORTRAN. And very few people like or are capable reading FORTRAN.
The theorem is "there's no injective function whose codomain is smaller than its domain". It's not stated this way because mathematicians are snobs or to impress students! abstraction is the very nature of mathematics.
From https://en.wikipedia.org/wiki/Abstraction_(mathematics)
"Abstraction in mathematics is the process of extracting the underlying essence of a mathematical concept, removing any dependence on real world objects with which it might originally have been connected, and generalizing it so that it has wider applications or matching among other abstract descriptions of equivalent phenomena."
Surely because that's history, we don't teach it that way because then you lose the links that have [much] later been found with other areas of maths -- isn't it the linking in to different areas that provides all the power? We want current students to understand a far wider curriculum and realise the links that come out of those abstraction, no?
I guess it's like whether you teach grammar to language students or hope that through language use they'll derive their own abstractions that allow them to understand the grammar sufficient to say things that they've never heard before.
From a history perspective we probably don't know how they came up with the idea, even if their journals (!) had a specific derivation of a proof then that wouldn't mean that was their initial direction of travel necessarily.
Also, yes, introducing the simplest version of a concept using examples before the most general version is a good thing. This is a recommendation commonly made in mathematics exposition. For instance Arnold, a Russian mathematician known for insistence on examples, introduces groups as a bunch of permutations closed under composition, and a manifold as smooth subset of R^n.
There are situations when the abstract definition itself has value, even for expository purposes. For instance, the abstract notion of a group or manifold or vector space helps one to understand which constructions are manifestly invariant under different coordinates. Linear algebra is all about understanding this point.
The same point appears in programming when the value of an abstract interface, which can be introduced by an concrete example, lies in the generality with which it deals with different examples. See Functor(Mappable), Monad, or Foldable in Haskell. A more common example is the Iterable interface which can be illustrated via a list, but the value lies in the fact that interface applies to many data structures.
Two more points - sometimes a concept is unsatisfactory because mathematicians haven't achieved a good understanding yet. It's just that the given concept is what was needed to solve some previous problem. Often future concepts, (which one learns later in one's education or newly discovered in research) clarify older unsatisfactory concepts.
Also, the aha insight that one gets that a seemingly abstruse concept becomes clear is often dependent on past work which has helped one to internalize some details. After the insight, just a couple of words can stand for long statements. For instance, the word 'manifold' stands for what would be a complicated notion for 19th century geometers, or a more simple example, 'local isomorphism' stands for a statement like inverse function theorem. But if one goes to a new student and repeats the insight, they may not get it as a certain amount of background work needs to be done.
Famously, for example, Bertrand Russell and Alfred Whitehead prove in Volume II of their Principia Mathematica, using theorem 54.43 from page 379, Volume I, that 1+1=2 (adding that "the above proposition is occasionally useful.")
Now, that is clearly obvious to everyone, and yet what Russell and Whitehead achieved in the intervening 400+ pages was more than just obfuscation.
Try to use mathematics to describe an artistic work. Or even precise muscular movement of a human arm in a ballet in its wholeness. Good luck with that!
See also Hempel's raven paradox.