Unregulated companies rate prospective tenants as good or bad using questionable machine-learning algorithms and big data. They don't give reasons for blacklisting a specific tenant. Perhaps their method gives them no way to do that.

The lack of clarity about the reasons for blacklisting would-be renters adds gratuitous frustration, but the basic problem is that rents are so high that workers struggle to afford them, so many tenants don't succeed in paying rent.

To make the algorithms more transparent would change who gets to rent an apartment and who does not, but would not prevent that the shortage. The only way to do that is to make a lot more housing.

The best way to make a lot more housing is to eliminate the zoning laws that prohibit dense housing.

As long as that does not happen, landlords will see that scarcity enables them to raise rents to levels that make struggle to afford the rent, which means that some will be unfortunate and get evicted, which means that landlords will seek ways not to rent to anyone who might have get into that situation.