Now, to make that happen, you need the oscillator to be
_almost_ decoupled from the rest of the world. In this
case, the oscillator is the U-shaped part. It doesn't
have to be U-shaped, but that shape is as good as any.
Then the handle attaches very near to a _node_ of the
fundamental oscillation.
If the handle attached anywhere else, the handle would
become part of the resonant system, and that would make
your hand part of the resonant system, and the next
thing you know, you've got no Q at all.
Symmetry is useful!
Mechanical disadvantage is useful sometimes!
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You see the same thing in electronic oscillators all the time.
If you have an LC resonator, the L is typically a transformer
or autotransformer with a humongous turns ratio, and you
couple to the thing via the tap on the winding, so that you
are only weakly coupled.