For words that can be a noun or not a noun, why does the noun have the emphasis at the start?

Solution 1:

This Wikipedia article discusses the origins of the initial-stress-derived noun:

In English, since the early modern period, polysyllabic nouns tend to have an unstressed final syllable, while verbs do not. Thus, the stress difference between nouns and verbs applies generally in English, not just to otherwise-identical noun-verb pairs. The frequency of such pairs in English is a result of the productivity of class conversion.

When "re-" is prefixed to a monosyllabic word, and the word gains currency both as a noun and as a verb, it usually fits into this pattern, although, as the following list makes clear, most words fitting this pattern do not match that description.

Many of these have first syllables that evolved from Latin prepositions, although again that does not account for all of them. . . .

When the stress is moved, the pronunciation, especially of vowels, often changes in other ways as well. Most common is the reduction of a vowel sound to a schwa when it becomes unstressed.