They're already working on doing exactly that. The construction work that the thieves hid with is to restore all the previous doors of the museum so they can start being used as entrances again to reduce the strain on the I.M. Pei pyramid, the modern entrance of the Louvre. Coupled with that, they're building the first temporary exhibit space of the museum, with an adjacent permanent exhibit space. That permanent exhibit's subject? Da Vinci and the Mona Lisa, with a special ticket to visit only that already in the plans.

In 10 years, bus full of tourists will go straight to the pyramid, then straight to the Da Vinci exhibit, take their goddamn selfie, and leave. The rest of the visitors will mostly enter through the historical entrances and never interact with those throngs of Mona Lisa lookie loos.

The Louvre is doing exactly what makes the most sense; they're not stupid, they're just not very fast, as is usual for a museum.