Despite the weight of the rack, mine is stated to be 230g, for what other reasons do people prefer seat packs rather than a rack n dry bag?

Looks better
Less likely to break?
Less likely to make annoying noises?
Encourages you to take less stuff
Works on bikes without rack mounts
Looks better

Not sure how many of those are valid reasons though.

Seen the odd rack broken by vibrations etc on longer rides, less risk with a light load but seatpacks may be more durable, generally lighter and can fit any bike. Rack and drybag works fine though, see any Iditarod bike pre 2007, John Stamstads bike for his pioneering GDR ride etc.

There was a thread on this only last week.

I found that the rack stiffened up my bike too much, as it didn’t allow the seat stays to flex.

Also weight, ease of breaking and ease of damaging the dry bag are why I go for a seat pack every time.