I ask solely about Anglo-American written judgments. Why don't judge's written judgments always comprise the headings "Ratio Decidendi" and "Obiter Dictum", just like how the headings "Material Facts" and "Issues" are always used to separate the Facts v. Issues?
This view appertains to each judge deciding a case. So if a case comprises 5 justices, there can be a total of 5 "Ratio Decidendi" and 5 "Obiter Dictum" headings that appear.
Obviously "Ratio Decidendi" will never be empty. "Obiter Dictum" can be empty if a judge has no obiter to "dictate", but always printing this heading will assist all readers to definitively distinguish what is ratio and obiter, and to forestall the following bafflements.
It is a mistake to suppose that every case has one and only one fixed and incontrovertible ratio decidendi. What exactly is the ratio decidendi of a case is often a matter for much argument. Also, the pick-lock art of distinguish depends upon a critical examination of all the facts of the case that might by any possibility be regarded as material.
7.8.2 Multiple and Inconclusive Rationes
It will not now come as a surprise that a case can be said to have different rationes in that there may be different interpretations of what is the proposition of law for which the case stands as authority. Equally, you need to be aware that: (i) even ‘crystal-clear’ judgments occasionally contain more than one ratio; and (ii) that in some cases no one can find the ratio.
Different formulations of a ratio
At section 7.3 we noted that a judge may reformulate the ratio by using different words later in his judgment. Th at certainly adds confusion but in many ways it is part of a normal thought process. Here, we have in mind a slightly different position—where a judge says: ‘I find for X for the following reasons . . . I would also say that there is another (unconnected) reason for which I find for X.’ Which is the ratio? This occurred in the Court of Appeal case of Turner v London Transport Executive  ICR 952. The traditional answer is that both statements are ratio . Later judges do not, however, follow a consistent line when dealing with such cases; they ‘relegate’ one of the statements to mere obiter dictum: see Lord Denning’s comments on Turner in Western Excavating v Sharp  ICR 221;  1 All ER 713 (also Court of Appeal). [...]
No clear ratio
We also have in mind a number of confusing cases which the lawyer usually relates as being ‘an authority for any proposition of law for which you care to use it’. This will arise where the judges are agreed as to the decision (X won) but present their reasons in quite different formulations. Bell v Lever Bros is one example.