The voltages where a gate input switches from low-to-high or high-to-low is affected by any noise on GND or VCC.

And the chips consumes extra power during switching.

Two oscillators running at different frequencies will have a resulting interference frequency, i.e. they will regularly get turn on/off times close to each other. And at these times, they are very sensitive to influences on GND and VCC. If the "bumps" on VCC/GND are long enough to span the difference in half-period time then the two oscillators can quickly force each other into getting in lock-step.

The closer the two frequencies are, the harder it is to manage to filter the supply enough that they will not interfere.

The capacitor in a RC circuit doesn't have any real "mass" forcing a constant frequency. If the gate switches 10mV earlier, the capacitor will happily accept that the circuit switched between charge/discharge that bit earlier so the frequency change can happen very quickly.

In the case of the pendulums, there is a mass in the system, so they required some time to transfer energy between each other before they managed to tune in to the same common resonance frequency of a single "super-pendulum".

An electronic design that have some form of "mass" can better manage the bumps in VCC/GND at the interference frequency. They still get their own frequency affected - there is more jitter in the output frequency - but the two oscillators must be much closer together in frequency for them to jump into lock-step.