Because his interest in, skill with, and love of language are manifest at every level and indeed in almost every word of LotR, thereby producing a result difficult if not impossible to duplicate.

       The previous question describes how Common Speech names were "rendered" into English. The Guide to the Names in The Lord of the Rings, Tolkien's instructions for translators, does attempt to address this. In it he goes down the list of names in the index and specifies which should be translated (being Common Speech) and which should be left alone. It would require skillful translation to get even this far, but that would only be the beginning. Reproducing the other linguistic intricacies described in the previous question would be well-nigh impossible; for example, Rohirric would have to be replaced with some ancient language whose relation to the language of translation was the same as that of Anglo-Saxon to modern English.

      On another level, there is the diction and style of everything said and told. The language used has a strong archaic flavor; it is not an exact recreation of how Anglo-Saxon or medieval people actually spoke but rather is as close an approximation as he could achieve and still remain intelligible to modern readers. This was not accidental but rather was deliberately and carefully devised. (See Letters, 225-226 (#171)).

       There were, moreover, variations in the style in which characters of different backgrounds spoke the Common Speech ("represented" as English) (e.g. at the Council of Elrond, FR, II, 2; see also RtMe 90-93). There were variations in the style of individual characters at different times (RK, 412 (App F, II)). There was even an attempt to indicate a distinction between familiar and deferential forms of pronouns (which doesn't exist in modern English) by use of the archaic words "thee" and "thou" (RK, 411 (App F, II); for an example, see the scene with Aragorn and Eowyn at Dunharrow, RK, 57-59 (V, 2)).

       Finally, there was Tolkien's poetry, which was often far more complicated than it appeared, and which in many cases is very probably untranslatable. (The extreme case is Bilbo's Song of Earendil, FR, 246-249 (II,1); T.A. Shippey has identified five separate metrical devices in this poem: RtMe, 145-146).