[yldstrk]

The name of the holiday is incomprehensible.

[DoodleBob]

It’s a portmanteau.

[jeffersondem]

“The name of the holiday is incomprehensible.”

As best I can tell it was probably named that by white people who were throwing-off on black people - implying black people were not smart enough to be able to count reliably in double digits.

I can’t think of any other explanation.

[ExSafecracker]

It is ebonics.