How come Esperanto doesn't have <favourite word or feature>?
Although Esperanto is a planned language, it has developed well beyond the point at which some authoritative person or group can dictate language practice, however great the temptation may be to "tinker" with the language. For example, many people are critical of the presence of a feminine suffix and absence of a corresponding masculine suffix, and have suggested masculine suffixes (-iĉ, -un, -uĉ, -ab), neutral pronouns (ŝli, hi, ri), and/or re-interpretations of familiar words, such as redefining frato (brother) to mean "sibling". But there is no single individual or committee that will simply dictate changes such as these before they achieve general use.
Just as with any other language, the only way for such novelties to attain acceptability is for them to be used in correspondence, literature, and conversation by a growing number of people. If you see a genuine lack in the language's existing stock of roots and affixes, you may propose a new coinage and see if it catches on. Be warned that such neologisms are often controversial and will meet with criticism in proportion to the extent to which they break with the Fundamento de Esperanto (the language's canon) or to which they are redundant to the existing language. You should expect to receive the same reaction as if you were proposing a new word or feature for your own language.