Entertainment agencies... some really only have nameless groups

It seems like there are a lot of them.
Of course, this might be because I know nothing about boy groups, but
seeing them constantly churning out groups
that can't even make it into the rankings of variety shows or music programs,
I wonder if they still make money?
Even when their businesses aren't doing very well,
I see some people launching multiple ones;
is it a strategy to take small bites out of the market like that;;
Usually, people who used to be celebrity managers become CEOs,
and it seems like the "Big 4" agencies dominate the system.
I wonder if the Big 4 maintain quality through massive spending
on talented people,
or if it's just due to their brand recognition.
It seems like an incredibly red ocean,
so it's quite strange how they even manage to survive.