While I don't think preservation of any commercially-released work should have to be justified, I think shovelware preservation is especially important because those are the historical context of many consoles, especially Nintendo. The average Wii experience was not Mario Galaxy and Rhythm Heaven, it was Ninjabread Man and Looney Tunes: Acme Arsenal - this doesn't mean everyone needs to be making passionate video essays about said games, but if someone 10 years from now wants to immerse themselves in the historical context of the Wii, they need to have these games accessible, and not just the greatest hits, to get the full picture - not in a backhanded "oh, that'll make you appreciate Twilight Princess" way, but in a "this is how most Wii players played Wii" way. The same goes for almost all of Nintendo and Sega's consoles with maybe the exception of the N64, the earlier 2 PlayStations, and a lesser extent for every other console
Note that the individual games named were simply used to represent the wider concept of shovelware, I am not suggesting that LTAA and NBM sold better than SMG or RHF, as much as just that more people played shovelware as a totality than the "timeless first parties" as a totality.
I mean in Japan, it was literally the first game with the Paper Mario moniker ("Paper Mario RPG", meanwhile PM64 was just called "Mario Story").