Why so many job boards get created?

My guess is that the employment market is a difficult market, every solution today does not solve it, and so people continue to try to build newer and better solutions.

there has to be something more fundamental or lower level that all of them are missing.

Let's say you're looking for a job, want to build your profile, want to know what skills are in demand, could use some side money, etc.

Building your own job board covers lots of different bases (possibly):

1) It's a good technical exercise and is a legitimate project you can point to during a job interview process and say "I built that".

2) It will give you first-hand exposure to available jobs on the market and / or what skills are in demand.

3) If it works out it could turn into an income producing project.

Basic function stacking - one project that potentially serves multiple purposes.

There's certainly a chance it won't work out. But for some I'm sure it does and has.

Job-posting data is bad. It's often unstructured walls of text with ASCII bullet points.

Programmers see this as a fixable problem and many are tempted to take a stab at it, only to realize that it's a much harder problem than it seems. Their solution doesn't fix the problem, other programmers think they can improve on it, and the cycle continues.