Why should instances of sc_module only be created from sc_main or a top level module?

[ramuneeb]

It states in section 4.2.2 of the SystemC Language Reference Manual that:

Instances of the following classes (or classes derived from these classes) may be created during elaboration
and only during elaboration. Such instances shall not be deleted before the destruction of the module
hierarchy at the end of simulation.
sc_module
(see 5.2)
sc_port
(see 5.12)
sc_export
(see 5.13)
sc_prim_channel (see 5.15)

What is the reason for this?

Why can't I for e.g. create an instance of an sc_module inside a C++ class?

[lmailletcontoz]

you can create an instance of an sc_module inside a C+ class, as long as this class itself is called from a sc_module or from sc_main. The primary purpose of elaboration is to create internal data structures within the kernel as required to
support the semantics of simulation. (see clause 4.2.1)