Why is eleven not pronounced onety one?

Because then twelve would have to be onety two and thirteen would be onety three and so on.

And twenty would have to be "twoty" and twenty one would be "twoty one" and etc.

It would be "Tenty-one", surely?

Then Tenty-two, tenty-three... Only it might become confused with "t[b]w[/b]enty-x" when spoken!

Strange question, but a lot better than some on SW! :-)

Because we're all cowards

it's kinda interesting that every language seems to have 'special' names for 1-20, then start with a pattern of [0-9] and [multiple of 10]

I think they first had only counting upto twenty, and for larger values they used to refer in units of unit (1 to 20) until the discovery of number system.

hahaha I couldn't pronounce it even now

Those grammar Nazis..

Excellent question! 🤔

It should be.