Longer words are not necessarily more effective, or more capacious, or more desirable. At the scale of human language, they are a finetuned adaptive vehicle. They sacrifice energy-, space- and time-efficiency for the sake of meaning. A long word exists because there is no other way. Like the exact distance between the Earth and the Sun. Too far and too long, and it would cool down in irrelevance, too near and too short and it would burn with too much compressed energy.
Or at least it should be like this. Rules are made to be broken. There might not even be any rules. Just the accident of formation, like the Alps, or the meanders of the Amazon.
Some words are misleadingly long. They are in fact compound words, like the German Freundschaftsbezeugung for ‘demonstration of friendship’, which Mark Twain found obscenely longwinded. We look for roots, and roots are short, though they go deep. The oldest English verbs are also the shortest, like get, let, be, do, go, run. Even the German word above is made up of Freund for friend and zeugen, to declare. The rest is mere spice, holding the ingredients together.
But words are long vehicles of meaning. They extend in time, they take up all the semantic motorway. It’s hard to overtake them because they keep the roadshow going.
In a language, decline occurs when its users forget where the words come from. Not everybody ought to be an etymologist, but the long vehicle of language should be on everyone’s radar.
I’m quite sure you already know this, but many German words are just shorter words strung together. Especially when new words enter the language.