Why does a for-yet loop not exist?

Question

I have learnt 4 kinds of iteration statements:

1. for (also called fori or forj)
2. while
3. do-while
4. foreach

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Why pray, then does a for-still loop, not exist?

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What are the use cases you ask?

1. Same question can be asked for a do-while loop, where we can just substitute it with an appropriate if statement surrounded by a while loop.
2. One use case I can think of is the following:
   (Just pseudo-code, 'cause well, this paradigm is language independent.

var stringToTokenize = 123,456,abc // expected output: string[] = { "123", "456", "abc"}

var token = "";

var[] tokens // (or string[], whatever)

// stringToTokenize will be referred to as str henceforth ('cause I am a lazy typist)

for(i = 0; i != str.length(); i++) {
    // token is complete, add to the array or list
    if (str[i] == ',') {
        tokens.add(token);
        //reset token
        token = "";
        continue;
    }
    token += str[i];
}

// one last time
tokens.add(token);

with a for-still loop this will become

for(i = 0; i != str.length(); i++) {
    // token is not complete
    if (str[i] != ',') {
        token += str[i];
        continue;
    }
    yet { // my made-up syntax
        // will run one last time
        tokens.add(token);
        //reset token
        token = "";
    }

}

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Is there something inherently wrong with this kind of construct of was it just thought of and dismissed?