I'm guessing they were looking for preferential delivery to certain cell types, and AAVs just happened to have best profile for those. If anything, LNPs might aggregate in the liver even more than AAVs, which can lead to even worse hepatotoxicity if an immune response happens.
Lipid nanoparticle toxicity has long been an industry concern.
In a profile of Moderna back in 2016, Katalin Karikó (instrumental in the development of mRNA vaccines) mentioned this issue:
“I would say that mRNA is better suited for diseases where treatment for short duration is sufficiently curative, so the toxicities caused by delivery materials are less likely to occur” [1]
