Why are most cleaners basic? (on the pH scale)
Supposing that you are reffering to alkali cleaners,well,first of all, it's important to know what alkali cleaners are used for. They are good at cleaning all kind of greasy surfaces, as glass, fiberglass , porcelain,stainless steel,chrome surfaces etc. The manner of cleaning is surface degreasing by removing and suspending the grease, which could be washed away by rinsing the surface, after degreasing.
The solutions of alkali cleaners could be more or less concentrated, they coming in a wide range of types: mild alkali (baking soda), moderately to strong Alkali(ammonia, borax, Tri-Sodium Phosphate), strong alkali (Sodium carbonate) and very strong alkali (Sodium hydroxide).
Also, as all substances, alkali are imposing cautions measures, knowing their effects. They could become toxic, or even lethal, if they are used combined with another cleaners, for example, ammonia could emit lethal gasses, or Sodium hydroxide could cause burns to skin and eyes and it has a high level of toxicity.
The chemicals for cleaning are selected on the basis of their ability to react with and loosen the material to be removed by the cleaning process without damaging the the basic object being cleaned. Because of this it is common to use either mildly acidic or basic material for cleaning. I do not have the statistics of the type of cleaning material generally used. However, if most of the cleaning material are basic, the reason for this will be that basic cleaners react easily with the material generally required to be removed by the the cleaning process, without damaging the items being cleaned.