The basic problem is that earning is done by meeting responsibilities within the bounds of rights. The basic problem is this: If there is no bedrock set of rights (or responsibilities to meet) one cannot define 'earning' properly, and one has no place to start earning rights (or accounting responsibilities as met).
Since rights and responsibilities are dual -- a responsibility is the lack of a right to refuse to do something -- it is easiest to focus exclusively on one or the other. Classical societies focussed on responsibilities, but since the Enlightenment, it feels better to focus on rights. It really does not make a difference, and I will stick with the language you started from.
In small cultures, rights are granted by those close to you, and earning is clearly if idiosyncratically defined. The bedrock right is the right of those in established positions to give out rights at will, but for those rights to go largely unchallenged once given. This leads to a great lack of uniformity and the hoarding of privilege. The system is more fair between those close together and less fair between those far apart. This is the ideal of the right, as it lets each person feel more fairly treated, even though there is massive underlying disparity that everyone ignores.
When one of these small cultures becomes too large, it becomes intractable to keep track of who has what rights in a way that does not fall back on the erratic and basically unfair smaller subsystems. The bedrock right comes to be the right to challenge all inconsistencies and demand compensation. A mediating system arises which starts off globally unfair by ignoring nuances and stripping away old earned rights.
By thwarting earned rights, such a culture often fails to inculcate a consistent set of values, and rewards clever manipulation or mechanical 'default' processing, instead. (The best-understood example is late Rome, with scheming patricians for whom life is an amoral game, played primarily by posturing on behalf of moralities they do not really hold, and dumb, pacified plebes, happy with their bread and circuses while the Empire provides those by grinding nearby peoples into slavery and poverty. This is the prism that political extremists would like us to see America through.)
The mediation produces the problem that bothers you in the question. Diffuse values create difficulty rewarding desirable behavior. In response, we keep adjusting the system back toward fairness in search of an optimal set of values that are easy to live by. This is the ideal of the left: a system that knows it is always out of balance, but keeps getting better overall by insistent tinkering. The focus on imbalance and correction, along with the continual change, makes everyone feel unfairly treated, even though they are all actually more equal, and generally better off on average, than in the smaller cultures.
I would propose that as we approach zero cost-of-information, we have the privilege of living in a world where these limits on large and small are no longer at odds. We can keep a lot of detail about populations and still address each case individually to some degree.
As it loses meaning this general trend of right vs left is getting highly conflicted and internally inconsistent. Politics is getting meaner and more rhetorically adversarial at the same time the actual agenda for people on the two sides are getting harder and harder to tell apart.
To me, this says we need different dimensions on which to focus our politics. 'Rights' is no longer the proper rhetorical base.