it is literally the cause in almost all case

Again stop using a term you don't understand. Failure to thrive =/= inadequate nutrition.

There are hundreds of reasons for failure to thrive. Inadequate calories and malabsoption are just two subgroups. Here is a more complete list. Keep in mind each group (In born errors of metabolism) can include hundreds of diseases.

Chronic Disease
    Cardiac
        Cardiac Failure
    Neoplasia
    Pulmonary
        Bronchopulmonary Dysplasia
        Cystic Fibrosis
    Renal
        Renal Failure
        Renal Tubular Acidosis
    Rheumatology
        Systemic Lupus Erythematosus
Congenital/Genetic/Neurological Disease
    Cerebral Palsy
    Craniofacial Abnormalities
    Fetal Alcohol Syndrome
    Intrauterine Growth Retardation
    Mental Retardation
    Myopathies
    Neurocutaneous Syndromes
        Neurofibromatosis
    Prematurity
    Primary CNS abnormality
    Genetic Syndromes
        Cystic Fibrosis
        Russell-Silver Syndrome
        Williams Syndrome
    Muscle weakness
        Prader Willi Syndrome
    Inborn Error of Metabolism
Endocrinological Disease
    Diabetes Mellitus
    Hypopituitarism
    Hyperthyroidism
    Growth hormone Deficiency
Gastrointestinal Disease
    Celiac Disease
    Chronic Diarrhea
    Chronic Emesis
    Esophagitis
    Gastrointestinal Reflux
    Inflammatory Bowel Disease
    Malabsorption
    Protein Losing Enteropathies
Infectious Disease
    Congenital infections
    HIV/AIDS
    Recurrent infections
    Parasites
    Tuberculosis
Immunological/Rheumagological Disease
    Immunodeficiencies
Other
    Anemia
    Heavy Metals
        Lead
        Drugs
            Amphetamine
            Cocaine
            Hydantoin
            Phenobarbital
    Dental Caries
Nutritional Problems
    Inadequate Calories
    Inadequate Protein
    Poor Appetite
    Maternal Malnutrition
Psychiatric Problems
    Depression
    Eating Disorders in Patient or Mother
    Munchausen’s Disease by Proxy
    Psychosis
Social Problems
    Child Abuse
    Caregiver/Child Interaction Abnormalities
        Emotional Deprivation
        Difficult Child
    Family Stress
    Parenting, Ineffective
    Poverty