You're going to read the configuration in a target programming language

So if the config format has its own type system you then have to convert between config types and language types

If the config type doesn't map exactly onto the target lang type you either ignore it and accept some values won't round-trip cleanly or without error, or you fall back to using strings (e.g. various possible integer type sizes, signed/unsigned etc, or decimal values via JSON)

Not saying it's always the right choice, but I can see why having lowest common denominator stringly-typed values as the config format can be seen as a feature allowing you to define the type system that the config will be parsed under to suit each particular application