This is because morphemes don’t truly exist in written English — they are just representation of a meaning that only exists in verbal form. In other words, written words exist to express spoken words which carry the actual units of meaning. The ideological building blocks of English live in spoken language, and those of mandarin live in the written language.
The letters in the word “explosion”, for example, don’t really carry any meaning in english except to phonetically spell out the sound of the word. The meaning is only stored in the spoken word. In mandarin the written word for explosion is 爆炸, made up of 爆 (the character for explode) and 炸 (the character for blast). Both of these characters have their own meaning and can be broken down even further into the symbols that compose them. 火, for example is the symbol for fire and is included in both characters.
If you think about where each language sacrifices unique definition it becomes pretty clear where meaning is stored.
Mandarin spoken syllables and words are frequently overwritten and overused (there are hundreds of homophones for each syllable and several for each word), whereas english spoken words are each nearly unique (minus deer and dear). This is because in Chinese, spoken language is only a way to express the meaning stored in written language. The Chinese language sacrifices spoken language specificity to better match the written words.
English letters are infinitely overused and morphemes endlessly twisted and obscured, making units of meaning in written english very hard to find. For English, written language is just a representation for spoken language. The English language sacrifices written specificity to allow for more abstraction and clarity in spoken language.