The * and the + swallow up all of the o's and replace them with a single e. This is called greediness, meaning that a pattern will match as much of a string as it can, maximizing the length of the pattern matched.

If you want ungreedy operators that work in the opposite way, use *? and +?. In your simple situation, a e+? is as good as a plain old e, so it's not really necessary. The added ? becomes more useful with character sets like [aeiou] for example. You might also want to see the perl man page on regular expressions (perlre) for more info.