Ironically, the simplest explanation for the apparent death of the 4-year cycle is the increased expectation for a 4-year cycle.

That is, the more there is an expectation for a blow-off top followed by a subsequent crash, the more desire there is to front-run both. Consequently, the bull starts earlier in the cycle (which was clearly observably beginning in late 2023 - roughly a full year ahead of 'schedule'); and then, as the bull really should be peaking, increasingly there will be efforts to front-run the subsequent bear (which would explain the muted bull we are currently observing now).