Healthy Exhaled Toxins aren't thought-about As bone (Waste product) Why?

We get rid of some amounts of toxins via breath. Then, why not exhaled toxins are considered as Mala – waste products as per Ayurveda? 

The concept of mala – waste products as per Ayurveda:
The total waste products are explained as two sets.
1. 3 main waste products
2. Waste products of different body tissues.
3 main waste products:
मला: मूत्र शकृत् स्वेदादयोऽपि च ॥
malā: mūtra śakṛt svedādayo’pi ca ||  – Ashtanga Hrudaya Sutrasthana 1st chapter
Mutra – urine
Shakrut – feces
Sweda – sweat are consider as 3 main waste products of the body.
They were grouped together based on high quantity.

4. Dhatu mala – waste products of body tissues:
किट्टमन्नस्य विण्मूत्रं, रसस्य तु कफोऽसृजः|
पित्तं, मांसस्य खमला, मलः स्वेदस्तु मेदसः||१८||
स्यात्किट्टं केश लोमास्थ्नो, मज्ज्ञः स्नेहोऽक्षि विट्त्वचाम्|
प्रसाद किट्टे धातूनां पाकादेवंविधर्च्छतः ||१९||
परस्परोपसंस्तब्धा धातु स्नेह परम्परा |२०|

kiṭṭamannasya viṇmūtraṃ, rasasya tu kapho’sṛjaḥ|
pittaṃ, māṃsasya khamalā, malaḥ svedastu medasaḥ||18||
syātkiṭṭaṃ keśa lomāsthno, majjñaḥ sneho’kṣi viṭtvacām|
prasāda kiṭṭe dhātūnāṃ pākādevaṃvidharcchataḥ ||19||
parasparopasaṃstabdhā dhātu sneha paramparā |20| Charaka Samhita Sutrasthana 18-20
The following are the malas (food) and dhatus (tissue elements):
Anna/ dhatu Mala(waste product)
1. Anna (food) yields stool and urine as waste products
2. Rasa yields Kapha (phlegm) as waste products
3. Rakta (blood) gives out pitta
4. Mamsa (muscletissue) kha-mala(waste products excreted from the cavities like eras, eyes, nose, mouth and genital organs)
5. Medas (fat tissue) –  sweat
6. Asthi (bone) kesa(big hair) and loma ( small hair)
7. Majja (bone-marrow) the unctuous substance present in the eyes, stool and skin
Thus, Prasada (nutrient fraction) and Kitta (waste product) these 2 categories of products arise out of the paka (metabolic transformation) of the dhatus (tissue elements). Therefore, the process of successive transformation of the dhatus is mutually inter- woven. [18-1/2 20]

So, why not exhaled toxins are considered as waste products (Mala)?

The Ancient Ayurvedic scholars did not consider exhalation of toxic substances as Mala. They were right in not considering exhaled toxins as Mala (waste product).

Mala is the one, which a normal human being excretes on a daily basis, which occurs as a biproduct of digestion and metabolism.

But toxins are not produced and expelled via breath in a normal human being. If there are toxins in the body which needs to be expelled through breath, then it is a Vikruti – a disease condition.

Ayurveda has explained this as symptom of a disease.

Durgandha shwasa – bad breath is told as a symptom of many diseases including Ama – a product of altered digestion and metabolism.