I do not have any argument opposing why we need only a single universal class. However why not we have two universal classes, say an Object and an AntiObject Class. In nature and in science we find the concept of duality - like Energy & Dark Energy; Male & Female; Plus & Minus; Multiply & Divide; Electrons & Protons; Integration & Derivation; and in set theory. There are so many examples of dualism that it is a philosophy in itself. In programming itself we see Anti-Patterns which helps us to perform work in contrast to how we use Design patterns. I am not sure, but the usefulness of this duality concept may lie in creating garbage collectors that create AntiObjects that combine with free or loose Objects to destruct themselves, thereby releasing memory. Or may be AntiObjects work along with Objects to create a self-modifying programming language - that allows us to create a safe self modifying code, do evolutionary computing using genetic programming, do hiding of code to prevent reverse engineering. We call it object-oriented programming. Is that a limiting factor or is there something fundamental I am missing in understanding the formation of programming languages?
Why classes implicitly derive from only the Object Class?
programming languages;type theory;object oriented
This is only an answer to answer the question in the title.Languages such as Java have every class deriving from Object for two reasons.Firstly, to increase the amount of polymorphism available. This was particularly required before generics were added to the language. Without Object,  collection classes would be impossible to write in a useful fashion. Secondly, there are many methods that classes are expected to have or are useful, and these are collected in Object. By ensuring that all classes inherit from Object, all classes will implement  the same minimal interface.As mentioned in a comment, C++ does not have a class like Object. C++ is in many ways untyped, so the issues I mention above are not applicable. Also, C++ templates provide a lot of polymorphism and are used to implement collections.