What motivates scientists to fabricate results in prestigious journal articles?
Only if you're either really (really) stupid or desperate, or naive enough to think that you'll never be found out.

The person in question here seems to have been a serial offender. And I'd be very surprised if anyone who offends so blatantly has no previous history. Fraudsters always start out small and relatively inconspicuous, but confidence and brashness grows until they're caught.

Yes, fraudsters seem attracted by the prospect of fame – but I can't grok why you'd submit a fraudulent paper to Nature. Seriously!? Of course you'll be found out! But no, it's not worth it. Ever.