It does seem to get more difficult as the average length of the words increases. I did a quick word count of your example sentence, looking for short words. Short words being words with 1, 2, or 3 letters only so that they cannot be rearranged. Your sample sentence was 29% short words. The original piece I posted was 46% short word, which was probably a big part of what made it easier to read. The short words provide the grammatical context and make it easier to guess the meaning of the whole.
I think you’ve put your finger on some of the reasons.