Missing English word

I am not a native English speaking person. My native language is Russian.
For almost half of my life, I enjoy English speaking environment.

It is handy to keep in mind series of words directly corresponding to each other.
Say, English WH question words have simple direct Russian translations:

English Russian transcription
what что chto
what...for зачем zachem
when когда kogda
where где gde
which который, какой kotoryj, kakoj
who кто kto
whose чей chej
why почему pochemy
how как kak

If I do not know an answer to a question
and do not like to go into details (say, because they are irrelevant),
I can reply by a single word.
In Russian, you just add a tiny suffix "-то" to the question word:

Question word Indefinite word
что что-то
зачем зачем-то
когда когда-то
где где-то
кто кто-то
чей чей-то
как как-то
почему почему-то

Let us try to translate this table.

English question word Indefinite word
what somewhat
what ... for somewhat ... for
when sometime
where somewhere
who someone, somebody
whose someone's
how somehow
why ???

In most cases, the indefinite word is formed by adding the prefix some to the question word.
Sometimes the question word is replaced by an appropriate noun:
For example, when is transformed to sometime,
rather than to somewhen.

But what to do with why? I really don't know!

In English there is no word somewhy.
But there is no any other word which could be used instead.
I desperately miss it!

I mean a precise replacement.
"For some reason" is not acceptable,
because "why" may refer not only to a reason, but also to a cause, accident, or whatever.

Really, I would appreciate any solution of this riddle.
Or explanation, why there is no solution.

Somewhy ?