See the Maharal in chidushei aggados. This is a summary.
The lesson to both R’ Meir and R’ Akiva (very next gemara) is that even when one manages to completely separate themselves (he ties how the yetzer hara appeared to them to the passuk lo bashamayim vlo me’ever layam) from a yetzer hara it is because they worked on it and more importantly the torah that they learned is a special protection for them. When Hashem removes that protection, they are as vulnerable as everyone else. In fact, the greater the person, the greater the yetzer hara.
Under normal course of events, R’ Meir would not be nichshol, but the lesson to him is, you still need the siyata dishmaya, maybe even more than the average person.
It would be an interesting tidbit to know if this incident with the satan happened before or after the incident with bruriah.