Why are mattresses made the way they are these days?

I just bought a new mattress, and am baffled by its construction.

It used to be that a mattress and “box spring” both had springs, and each shared in making a bed comfy to sleep on.

My new mattress is 12 inches thick, while the “foundation” is just a fancy wooden box (also 12 inches thick) that serves no purpose other than to make the bed an uncomfortably high altitude above the floor.

Maybe there’s some logic to putting all the springs in the mattress itself and doing away with the “box spring.” But why, if the foundation serves no real purpose any longer, does it exist?

I could have saved a ton of money by not buying a foundation and setting my mattress on a pair of plywood panels resting on the bed frame. It would have made no difference to how the mattress feels when I’m sleeping, and I’d have been lower to the floor.

Sometimes I feel like I need a ladder to climb into bed.

Anyone know the rationale for current mattress designs? Especially someone who works in the mattress industry?