According to Mahayana, the meaning of Dharma is metaphorical or expedient ("upaya") - and you are taking it literally.
In my understanding of Mahayana, -- and it is very clear to me that this is how the original Buddha meant it as well -- things like reincarnation, liberation, karma etc. all refer to informational, psychological, and ethical aspects of reality - and not to some fairy-tale fantasies.
According to this interpretation, there is no literal "afterlife" (it's not even a concept that ever occurs in Buddhist texts!), there is cycling of forms - generation after generation, carrying same patterns along in a self-perpetuating way. There is no "cosmic law that liberates" and "is eager" - there is natural evolution towards greater awareness. (In the modern science these natural laws are beginning to get described in the emerging discipline of "biosemiotics")
So if we look at it from this perspective, why would the natural laws care about "beings be given ability to observe and realize the truth about samsaric worlds"?
Regarding the chicken and egg problem you are describing (that, for the sentient beings to get serious about Liberation, they'd need to clearly understand the problem, but according to Buddhism a clear understanding of the problem is only possible at the very end - almost at the time of Enlightenment itself, which makes it a vicious circle) - this has unfortunately been an issue with Buddhism all along throughout its history. Because the root cause of the Problem is Ignorance, there is no easy way to approach this issue.
Over the centuries of experimenting, different schools developed different methods, ranging from trying to explain everything with the hard logic upfront - to using informal hints to carry the gist of the Vision across - to asking the student to take it on faith and focus on practice until they get clear enough to start seeing it for themselves - to feeding the student with expedient fairy-tales as a child-friendly carrot effective as a temporary surrogate for the actual understanding.
So your concern and confusion is completely appropriate and well-based. Unfortunately, there are no easy answers to this (outside of the tongue-in-cheek "trust Andrei he knows what he's talking about") - or else you are on your own in this sea of doubts, trying to figure out what is what from the all the million voices screaming at once.
Fortunately, Buddhism does not require you to understand all this in order to get the basic ground under your feet and start making meaningful progress. All you need to do is understand the following basic framework:
Pain feels bad, peace feels good - at the end of the day this is what really matters. Stupid actions lead to inner pain, smart actions lead to inner peace (long-term; short-term there could be temporary roundabouts). Stupid/painful is by its nature is polarized, black-and-white, selfish, greedy, and leads to conflict. Smart/peaceful by its nature is all-encompassing, sees things from all sides, altruistic, and leads to reconciliation of positions. Start acting smart and don't act stupid and soon enough you will see the benefits for yourself. There is no need to be Enlightened to understand that if you create peace, you will get peace and if you create pain you will get pain. - this is sort of self-evident and is all you need to practice Buddhism.
Basically, the above was the gist of the answer Buddha gave to the confused folks as depicted in the Kalama Sutta. Don't worry about "Samsara" and other metaphors.
To avoid all evil, to cultivate good, and to cleanse one's mind — this is the teaching of the Buddhas.
- The Dhammapada: Chapter 14