Do people associate Italian with quality?
Certainly thinking back to the 90s Italian cars had a pretty atrocious reputation IIRC, and as for Italian restaurants they tend to err towards greasy spoon IMO, even if personally I quite like the food.
It's not like Avanti seems to have any kind of meaning which relates to rail travel. Virgin got away with this as it was (and is) a well known, well established and generally respected - if slightly contentious - brand. Something like Abellio is similarly meaningless, and it's notable they dropped using the brand name on AGA, which is now plain Greater Anglia.
The other problem with brand names is that they can go badly sour if things go through a rough patch. Connex is still remembered as a distressed brand even though they've been absent from UK rail operations for 15 years or so now. Whereas a plain geographical brand is, IMO, much more likely to recover from a rough patch, as Southern largely has.