I’ve added a few lines to your code. That’s sufficient to make it clear why this is disallowed:
void f(vector<const T*>& p)
{
static const T ct;
p.push_back(&ct); // adds a const T* to nonConstVec !
}
int main()
{
vector<T*> nonConstVec;
f(nonConstVec);
nonConstVec.back()->nonConstFunction();
}