There are way way too many swimming events. Why do you need 4 different strokes? Its like having the 100m run, the 100m hop, the 100m skip and the 100m run backwards. No one should even have a chance to win 8 golds.
There's hurdles and the walk.
And not many swimmers are top-class in several strokes.
Look at the field events. The decathlon etc.
There's shot put, discus, javelin, etc.
It's possible in athletics to win 8 Gold Medals as well - no one has, but no one has won 8 in swimming either.
And look at track cycling, which is also possible to win 8 Gold Medals.