... because they are so jaw-dropping in their intricacy, and so it's fun to see how far we can take it.
If this model wasn't simply a plausible theoretical explanation of the quasi-biennial oscillations, it would also make for a practical heuristic.
Most of the fit is the result of the aliasing of the Draconic or nodal month of 27.21 days (aliased to 2.36 years), but the other known lunar factors contribute as well. Important that these are the same periodic factors that go into well-established length-of-day  and ocean tidal prediction programs, but are aliased to show resonance or amplification with the seasonal cycle.
Taking the second derivative adds much more structure to the profile, yet the same set of factors continue to provide a more than adequate fit.
The QBO is an example of a forced-response system. The natural response could be buried in there as well, and may even be the hazily-attributed 2.96 year cyclic factor indicated above, but the weight clearly favors the known lunar gravitational forcing factors.