Am I doing something wrong?
There are a few things you could have done that might have helped, but you did more than the instructions ask for. And from what we can see, you didn't do anything directly counterproductive (such as moving the stripper around when it's supposed to be sitting undisturbed, one of the three most common stripper faux pas).
Why isn't the stripper removing the finish?
Because it's not good enough for this finish. Kudos to Fully/Jarvis for choosing a really top-notch finish!
Although I'm familiar with its type I have no idea how good this Klean Strip stripper is overall. Despite the label specifically claiming it can work on epoxy and polyurethane1 many (perhaps the majority) of modern non-MC strippers barely touch, or seemingly have zero effect on, a few modern coatings. This includes but isn't limited to: UV-cured products as here, two-part urethanes, polyesters, epoxies and various "2K" finishes.
It is possible that if you could leave the stripper on for much much longer than directed (while keeping it from drying out) it could begin to work — in a similar situation I've had some success leaving a very generous coating of stripper on for a full day, twice2 — but this is much easier to arrange on smaller items.... and at the end of the day there's still no guarantee it'll do enough to make the effort worthwhile.
So what now?
If you do decide you need to continue to remove the finish (but see below) I suggest you do look at alternatives, principally scraping as I aim you to in the Comments above, assuming you don't want to try a different stripper type.
am trying to darken the finish
Since this is your end goal a headsup is in order.
Bamboo is typically slightly denser and harder than sugar maple/hard maple and just like maple it does not typically stain well (staining conventionally) because the high density makes it resistant to stain penetration.
As a result a coloured overcoat, such as "gel stain" (despite its name these are jellied varnishes) may be preferable to give you the result you want.
An added advantage to using such a product is the original finish does not need to come off first. As long as the existing surface is clean and matt subsequent finishes should bond to it acceptably well. See Good methods for scuffing/sanding ready-built furniture with contours for repainting for a little more detail.
1 For the record, I'm dubious.
2 And it still didn't remove all of it!