What's up with RPM
How is it they have the same max RPM? Shouldn't more power mean higher speed in the absence of other variables (e.g. weight)? What is the extra current spent on if not speed? Torque? Or is the extra current only drawn under load; in response to a physical resistance (i.e. drag) on the driveshaft?
They're the same RPM because they are induction motors. (also would be equal if they were synchronous motors).
What you're expecting is series-wound or shunt motor behavior. These are DC things, which add a great deal of maintenance or complexity: Brushes.*
Remember -- this is AC power. It came from a spinning generator. The 3 phases are already rotating - peaking in sequence: A-B-C-A-B-C. A motor is simplicity itself: 3 windings in the stator, wire them up to each phase, and now you have a rotating magnetic field in the stator. It is rotating at 50 Hz, the agreed AC line frequency.
(we'll come back around to the single-phase wrinkle).
So with the stator rotating at 50 Hz (or 25 Hz if you have wound it with double the poles), the rotor is simplicity itself. A permanent magnet would give a synchronous motor, but even cheaper, a trick with induction lets you use an entirely passive aluminum "squirrel cage" rotor, giving nearly synchronous speed.
If you can live with 2880, 1440 or 720 RPM, it's cheaper* all around.
With single-phase, it's like bicycle pedals - If you start a bike with the pedal at absolute top, it won't go down - sideforce is needed to start it, but once in motion it is not needed. That's what the capacitor and extra winding do. Again once the motor is spinning it is not needed.
Anyway, you are correct that the extra current is not drawn unless a load is placed on the motor. At that point, the motor will bog -- or not -- depending on if it can handle the load.
The motor has a torque max around its stated frequency (e.g. 1440 RPM). Below that, torque gets worse and worse. If you've ever pushed the limits of a table saw, you are well familiar with how easy it is to bog or stall the motor by asking too much of it. The load (machine) needs to be designed to be suited to this torque curve. This is why trams and electric trains don't use induction motors (at least, not without a VFD).
When you need a motor that "downshifts" and makes more and more torque, you need a DC series-wound motor, which is what trains use. Or a VFD tuned to have the same effect.
Size
A motor of twice the power needs twice the mass of copper windings.
It's pretty much that simple. They are making twice the magnetic flux, or so they say**. Whether it's longer or thicker wire makes little difference. (longer wire most likely means they are paralleling).
Without the shaft (compute L - E), the motors are 156 dia x 255 length, vs 174 dia x 295 length. So one motor is 6,205,680 cylindrical mm and the other is 8,931,420 cylindrical mm. That's considerably less than double the package size, but given the things that don't need to expand such as case thickness or rotor diameter, that may be about right.
* Unless you really, really, really want to do a Variable Frequency Drive, using silicon to convert AC to DC then back to AC at any frequency you want.
** And these motors are cheap Chinesium. Notice the obvious misspelling in the lower label, and the "weird font" in the upper. That's a Chinese language font, in a style fit for Chinese characters, which includes the 52 Roman letters done in a matching style. Also the prominent CE mark, which they fake because there are no consequences for doing so, unless your boots are inside the EU.
*** In North America, 60 Hz, 3450 RPM, 1725 RPM or 885 RPM.
