Different Writer Aliases

I'm currently reading The Fell Sword by Miles Cameron. When I first found the series, I read many reviews claiming that it was a great debut for Miles Cameron. However, it wasn't until half way through the first book that I realised that Miles Cameron was just Christian Cameron writing under a different alias and that Christian Cameron was actually an author who had written several other books and series, including one he wrote under a third alias.

This is the second time I've read a book whose author was writing under an alias and I'm just wondering why do experienced authors do this? And do people just not realise it's an experience author writing with a different name?

Probably because as an established author with a large reputation, any new book they write will have a certain high level of expectation. Especially if they are writing a new topic, they may want to make a fresh start, free of any conceived expectations from readers.

If they're famous for another reason, they may also want to use an alias; if justin bieber wrote a book called 3rd Century Crisis, a Complete Detailed Historiograpy, you wouldn't take it at all seriously. However, if the same book was written under D.H Johnson, then you'd certainly give the book more than a passing glance.

If you look closely at the language used, you may be able to tell if it's the same as another author, thus they're the same person. But most people probably wouldn't.