The overriding aim of most formats was to load into memeory efficiently - fast load times was the key winner in the 80s and 90s. So you did not want a simple serialisation because that meant slow CPU intensive save and loads. But if you slammed it in pretty much as it would be in memeory you would win. Downside is if you change the in memeory representation of the running program you had to change the file format.

And .mov would have no such concerns - it's prime use case is store data in serialised chunks anyway - it was already serialised so could use very dumb stores.