I've actually gotten this question quite a lot (well this and people asking if Tanya will return >.<), and this was as good of a time as any to answer it. In Day of the Eevee, Todd became an espeon through the overwhelming loyalty and love he felt for all of his friends who would always be there for him. There is no good reason to trash all of that by having him abuse his powers on his friends. That's not how espeons are known to behave and it goes against the emotions involved with Todd's change.

I don't mean this to become a lecture. I'm just saying... I'm sure we can all agree that there was always more to Todd than just acting out with pranks and causing trouble. He became an espeon because he saw that he didn't need to act out to gain the attention of his friends anymore. That he himself was what mattered to them. <3