They don't NEED to be insanely expensive, they are mismanaged and over scoped, and you often hear how they totally scrap everything multiple times during dev (ie mismanaged).
Even so, they can be wildly successful, just with lower peaks than the top GaaS, many are profitable but not massively, just sustainably. Even failures, they fail but still usually make a lot back….its not like they spend 200mil and make 2mil, then delete it from existence, many can have long tail and eventually become profitable. There are some high profile massive failures like veilguard but rare.
Gaas, they still spend a fortune on, and the overwhelming majority are complete and utter studio killing failures. A Gaas failure makes almost nothing, and ceases to exist after it fails. No long tail, high ongoing maintenance cost. It's rambling with extremely poor odds and everything (including everyone's jobs) on the line. Chasing that high is literally killing the industry.