Back in my day you had to level the bed by hand! We had to put a piece of paper between the print nozzle and the bed until the gaps were perfect. If the bed was warped, there was nothing you could do!

The Bambu will have some sort of auto bed leveling. The simplest method is a limit switch connected to a small plunger style probe mounted next to the nozzle.

Whatever the specific method, the idea is something that lets the printer sample multiple points on the bed and use the Z axis dynamically to adjust for the small irregularities. If you don’t have that, even half a millimeter can ruin print quality, so the leveling screws are there to handle it manually from the bed side.

BambuLab wants to be the Apple of 3D-printing. So they simplified and decided the factory bed level with auto bed leveling/compensation is good enough for the user.

On high end printers there is just no need to level them. The factory does it and the bed won't move at all due to the excellent mechanical designs.

Everything else? They have it to level the corners of the bed and use automatic bed leveling/correction to get it perfect and adjust for build plate imperfections.

There is one system that does level the bed but doesn't need the knobs as each of the three mounting points is connected to an independent z-axis (kinematic bed): https://www.youtube.com/watch?v=bgkK7Fez8VU

It's worth noting that there are a few bed leveling methodologies:

• Full manual, such as the stock enders of yore
• "Automatic leveling" without a means of actually getting the bed in plane with the gantry. An ender with a touch sensor falls into this category. So does the X1 actually, since the three lead screws share a common z motor. As the bed gets out of plane with the gantry and/or your bed warps the printer will compensate. Ideally the bed and gantry are designed in such a way that they can't become that out of plane (for example, the bed is fixed)
• "Automatic leveling" with a mechanical mechanism to get the gantry and bed in parallel planes. This is what Vorons, Rat Rig, etc do. They'll also benefit from a bed mesh, since most beds aren't perfectly flat

I can't even get my Ender 3 level with the screws anymore.

My x1c still has nobs below for manual leveling?

I don't know the Bambu model, but I do have an ender 3 and a prusa mk4. The ender 3 out of the box doesn't have an auto leveler, it is "dumb" and it assumes the level of the bed is correct (if you leveled it right it should be).

Other printers like the mk4 and I'm assuming the Bambu have auto levelers that sample the level of the plate over several points, and then remembers the height of these points. Because it remembers the heights, it can adjust for a bed that isn't manually leveled, so there's no need for knobs.

You can get this functionality for the ender with a bltouch. But you'll have to enable it in the firmware and do some configuration and wiring. It's not too hard.

I replaced the springs on my Ender 3 Pro with Bed Stiffeners when I added a CR Touch. There is no need to level the bed anymore