Engine oils are constructed with built-in protection against acids. During combustion typical in any engine the sulphur present in the fuels (probably air too) oxidises in the presence of oxygen and moisture (H20) and temperature/pressure to form weak sulphurous acid/Nitric acid. This further oxidizes in the presence of temperature/pressure to become stronger and stronger till t becomes a full blown Hydrochloric or Nitric acid.
This reaction needs to be neutralized and is done by TBN additives, which are sacrificial in nature., i.e. get depleted over time.
Industrial gear and Hydraulic systems do not encounter combustion, which require fuel (including Sulphur) or Air (Nitrogen), however the pressure and temperature may be at par. Consequently Industrial Gear and Hydraulic oils have Anti wear, extreme Pressure additives built-in to the formulations, but not TBN additives.
The severity of the typical engine oils operation with combustion/explosion/temperature and pressure and Sulphur in fuels that it demands a countering through an anti-acid package or alkalinity known as TBN.
In comparison, the severity in Hydraulic and Gear Oils can be met through treatment with oxidation inhibitors. hence, TBN package is largely uncalled for, due to lesser severity.