Why rare species of apex predators evolve

[Hybridfish7]

Just as an example, I will use vazzoleri and fogo. As everyone knows, they are extremely rare. However, I was wondering, how and why rare species of cichla evolve like this. Cichla would just be an example, as there are other apex predators that evolve in similar circumstances. The circumstance being, an environment where there are different species of predators that fill the same niche evolving alongside one another. Are they rare because their populations are naturally small as a result of them being evolutionary offshoots that somehow became species and are on their way to extinction because of outcompetition from more numerous and successful species that fill the same niche, at least within a couple hundred-thousand years?

 

[Milingu]

The different cichla species evolved from geographically separated/ isolated populations that could not share their genes with other populations while at the same time adapting more and more to their habitat.

A species being rare does not automatically mean they are getting outcompeted. It can have many reasons. For example they can simply live in a smaller habitat or in a habitat with less food per area resulting in less specimen in the population ( = making them rare) while still being a successful species.
So the question should be why we consider for example fogo as rare?
Is it just because their habitat is hard to reach thus making them only rare in the hobby, or because their habitat is small, or because their population is less dense compared to others?

Cichlids are one the fastes evolving group in fishes. So I don't think another non-cichlid species will outcompete them as long as there is no severe influence on the ecosystem from outside like deforestation, climate change, invasive species brought by humans etc.

By the way I would not consider cichla an apex predator. They are huge but there are still other animals that will eat them if they can get hold of them.

 

[FJB]

It is typical of trophic chains that apex predators are much, much less abundant (i.e., "rarer") than other, more basal elements of the web. Otherwise the trophic system would not operate as it would run out of lower levels to support the higher.
In some (comparatively fewer cases), higher level predators may appear to be very abundant (think a traveling cardumen of tuna), but this is only locally and changing in time and space (i.e, migratory), following vastly abundant, also very mobile prey. In more localized systems (i.e, not as mobile at the large scale), the system will quickly collapse if top predators would be abundant enough to deplete their food source.