Spellchecking “amateur” (from “ameture”)

My brain is somewhat fucked in a number of ways. One of those ways is dealing with words – yes, reading and writing.

A specific problem I have is remembering the spelling of a handful of words I use semi-regularly.

And one of those words is “amateur” (correct spelling).

After a time I ways revert to spelling it as “ameture” (incorrect spelling).

I know this is incorrect, and every time I wait for software spellcheckers to pick it up… and every time they fail.

Which begs the question: what is wrong with spellcheckers?

Surely the incorrect spelling is close enough to the correct spelling – in both sound and structure – to have a common rule?