The Maharsha explains that the rationale for darshening every "es" in the torah is to show kavod hatorah by proving that there is no extra word or letter (as rashi explains at the end of sotah, when r' akiva died batla kavod hatora). But, when shimon ha'amsuni couldn't darshen "את ה' אלקיך תירא", he retracted from all of them and commented that just as he received reward for showing kavod hatorah by darshening every word, he also received reward for showing kavod hatorah that nothing can be equated with yir'as hashem. However, R' Akiva held that including talmidei chachamim also showed kavod hatorah.
The Chasam Sofer (pesachim 22b) also has a beautiful approach to this gemara. Shimon Ha'amsuni realized that the pasuk can be darshened to include talmidei chachamim. However, he was concerned that this would force the explanation of את ה' אלקיך תירא to mean Yira'as Haromimus - awe for the greatness of Hashem, rather than fear of punishment, since fear of punishment is not applicable by talmidei chachamim. He was afraid that by publicizing this drasha it would scare people off and intimidate them, since most people can't achieve this high level of awe. He abstained from this drasha and declared that since he is abstaining l'sheim shamayim, he will receive reward as if he publicized it. However, R' Akiva who came from nothing, and accomplished everything, personified the ability to have achieve incredible heights in yir'as hashem. He was able to publicize the derasha because when people will see what he accomplished they will be more encouraged rather than discouraged by the difficulty to achieve yira'as haromimus.