Design unnecessary complications

I have always wondered why commercial circuits are overly complex with a lot of ICs.
Take for instance a client brought in a display controller with a faulty card. Looking on the board with about 200mm x 200mm size, I notice nothing less than 10 ICs, a lot of discreet component. We eventually designed a new circuit board to replace this using only PIC16F876A as the integrated circuit, few passive components.
And that get me wondering why the circuit was that much. Could it be some objective redundancy design or the company making this want it to look costly to the client?
For today I find myself doing a design for another client and I was eagerly trying to minify my design to save production cost, then it occurred to me to ask why most commercial board are designed contrarily.

If it ain't broke - don't fix it.

Why risk a whole new design, when the old design is doing a perfect job.

... unless space, obsolescence or some other factor makes a change of design worth the effort...

How will you prove that your new design is more reliable than the old design? (if reliability matters) and how much will it cost to prove it?

research "cost-benefit analysis"

It wasn't doing a perfect job. I said it has a faulty card.
That was just an instance, not the question I asked

And reliability? Yes it has been running over two years now and still is. If two years is enough of that claim, though.