As stated in esperanto.net FAQ
About 75 % of Esperanto's vocabulary comes from Latin and Romance languages (especially French), about 20 % comes from Germanic languages (German and English), and the rest comes mainly from Slavic languages (Russian and Polish) and Greek (mostly scientific terms).
Is there a historical reason for that?
French was the world language prior to the second world war. Latin had great influence in the national school systems. And in scientific nomenclature. Slavic languages were not in high regard. Germany was central in Europe.
French was modern, trendy. Letters by air mail were "PAR AVION," the hair stylist was coiffeur or friseur. Children of the well-to-do were taught French. Pretty the same as today kindergardens with English.
But the influence on Esperanto of French is still moderate. The romance languages were a bit overrepresented considering demography and if you count scandinavic languages and 50 % English to the germanic group one arrives at 60% romance to 40% germanic. Where of course words like regulo represent both groups.
One influence was the growing vocabulary of Esperanto in those times: the word makers. There is a cultural influence whether beach becomes plaĝo (French) or strando (German). There certainly was no linguistic coordination like one might expect from Interlingua.
There also is the hypothesis that German uses compositions as in Esperanto, and hence is not so rich in root words, and the words are too ambivalent. "sich langweilen" por "enui" - estus malfacile tiun ŝtonigitan vortformon rekrei en alia formo. And a choice between laugh: "ridi" - rire or lachen is likely to be in favor for the romance.
At this point the slavonic languages should be given a minute of silence.
One additional point to the Joop Eggens great answer, which explains the topic to the most part.
Please read Claude Pirons book "La Bona Lingvo". There, the author complains about the over-romanization of Esperanto. According to him, Frenchmen tend to unnecessarily borrow the words from the French language instead of using the Esperanto word creation system.
The most known dictionary in Esperanto, the PIV was created by a french linguist Gaston Waringhien. Hi did a great and important work, but on the other hand, there are also many topics which were criticized by Piron. This point is controversially debated until today.
