Well I think the drama around it might have helped, but as someone who has done art history, I can’t remember the stolen part being mentioned.

Leonardo seems to be very famous in his time and after, and he died under the patronage of the king of France. I highly recommend reading his notebooks, it gives a glimps of the mind of this genius. His observational skills were impressive. In a way he was a hacker if you take the expanded meaning of the word: always thinking up new things and inventions.

And at the time it was stolen, image reproduction techniques capable of displaying artwork in at least recognisable fidelity within mass-market publications were just being introduced. (The distribution of such images probably also reduced the effective value of the work-as-stolen as it would be more readily recognised if displayed publicly.) Attention returned repeatedly to the Mona Lisa through numerous subsequent events, e.g., Duchamp's reproduction with a beard and mustache added, in 1919.

<https://www.britannica.com/story/why-is-the-mona-lisa-so-fam...>

<https://www.wikiart.org/en/marcel-duchamp/l-h-o-o-q-mona-lis...>

Google's Ngram viewer suggests a further increase of references in print following 1980, though that might reflect a disproportionate presence of academic works within the scanned corpus:

<https://books.google.com/ngrams/graph?content=Mona+Lisa&year...>