Are you perhaps ignoring the individual state taxation systems of the USA (not federal which is CY)?
"Forty-six of the fifty states set their fiscal year to end on 30 June"
https://en.wikipedia.org/wiki/Fiscal_year#United_StatesI think you can probably look at things like Californian state EV subsidies, taxes and rebates etc as being the driver for that end of fiscal year spike,
just as @Dancing originally posted.
