Currently providing mapplets to google means providing content for
free and gaining some traffic / visibility for the content provider,
but also loosing earnings because users can use mapplets to access
data/information without visiting the provider web site (where lot of
editors have advertising incomes).

Giving the opportunity to receive revenues from mapplets (with ads
layer) would push lot of content provider to build better mapplets, in
a similar way to how Facebook let developer build business on Facebook
Applications using FB's API and platform.