The question "How do we started to count by tones, instead of semitones?" is more practical but the meaning of what I mean is actually better reflected with the second question. Another formulation would be:
  Why wasn't the smaller "leap", the "semitone", taken as the unit (and then called "a tone")?

We say there're 6 tones in an octave and then that the distance of the notes of major scale (for example) jump 1-1-1/2-1-1-1-1/2 tones.

Why wasn't what is known as "half tone" called a tone since the beginning, as a tone is not any unit whatsoever? Using the actual semitone as a unit, i.e. as a tone, we would have and octave with 12 tones and then simply show that the the "leaps" go 2-2-1-2-2-2-1 tones.

Is there a practical rationale for things not being this way and being the way they are? Are they this way merely for arbitrary or historical reasons?

A more practical formulation of the question is "Why do we count by tones, instead of semitones?", but its meaning could be misinterpreted; the target of the question is actually on the concept of "1 tone" as a unit: "Why wasn't the smaller "interval leap", the actual semitone, taken as the unit and therefore called "tone" (or "one tone")?

We say there're 6 tones in an octave and then that the distance of the notes of major scale (for example) jump 1-1-1/2-1-1-1-1/2 tones.

Why wasn't what is known as "half tone" called a tone since the beginning, as a tone is not any unit whatsoever? Using the actual semitone as a unit, i.e. as a tone, we would have and octave with 12 tones and then simply show that the the "leaps" go 2-2-1-2-2-2-1 tones.

Is there a practical rationale for things not being this way and being the way they are? Are they this way merely for arbitrary or historical reasons?

The first question in the tittle is more practical but the meaning of what I mean is better reflected with the second. Another formulation would be:
Why wasn't the smaller "leap", the semitone, taken as the unit?

We say there're 6 tones in an octave and then that the distance of the notes of major scale (for example) jump 1-1-1/2-1-1-1-1/2 tones.

Why wasn't what is known as "half tone" called a tone since the beginning, as a tone is not any unit whatsoever? Using the actual semitone as a unit, i.e. as a tone, we would have and octave with 12 tones and then simply show that the the "leaps" go 2-2-1-2-2-2-1 tones.

Is there a practical rationale for things not being this way and being the way they are? Are they this way merely for arbitrary or historical reasons?

The question "How do we started to count by tones, instead of semitones?" is more practical but the meaning of what I mean is actually better reflected with the second question. Another formulation would be:
Why wasn't the smaller "leap", the "semitone", taken as the unit (and then called "a tone")?

We say there're 6 tones in an octave and then that the distance of the notes of major scale (for example) jump 1-1-1/2-1-1-1-1/2 tones.

Why wasn't what is known as "half tone" called a tone since the beginning, as a tone is not any unit whatsoever? Using the actual semitone as a unit, i.e. as a tone, we would have and octave with 12 tones and then simply show that the the "leaps" go 2-2-1-2-2-2-1 tones.

Is there a practical rationale for things not being this way and being the way they are? Are they this way merely for arbitrary or historical reasons?