Why weren numeral words selected so that if sorted in alphabetical order, a number would also sort in numerical order?
The idea likely didn’t occur to the designers at that time. Also, the common way of assigning series of cmavo (grammatical words) is to have the initial consonant the same, but vowels in ascending order (a, e, i, o, u; or i, a, u). Doing this with numerals is not possible, because there are more than five of them. Also, an important principle in creating Lojban numerals was that they were to be maximally distinct.