how does this tub drain work?

Water is not going down the drain quick enough, so I played with the drain lever. It wouldn't budge. I took it off and it's corroded solid and was no longer connected to anything.
Looking in the hole, I see two metal rod things. I pull on them expecting a metal cylinder to slide up and out, like I've seen in other tubs. But it won't pull up. I used pliers and pulled pretty hard but didn't move it.
How does this work? Is it just corroded stuck?

The trip lever sticks through those to flanges and has a cotter pin to join them. Your cotter pin broke off, try a paper clip. You need to pull the trip up and out of there to put it all back together

You have to pull on it very hard . If it won't come out you have to replace the whole waste and overflow

I pulled on it very hard. Using the pliers as a lever on metal edge of the overflow, I uncurled the lift wire hook, pulling out the linkage and wire but not the plunger.
So I replaced the entire waste and overflow.
Thankfully it was all very easy access from the closet behind it and the basement. There was a drum trap I replaced with a P-trap too.
This is an estate home I'm selling, and the bathtub and bathroom are crap so I went cheap on the new parts.
Fyi, the Home Depot cheap $29.99 pvc 1-1/2 in. Plastic Bath Drain Kit works, but had to be extended to the very very limit for this old cast iron tub.