We are talking about guest dresses for a wedding, why do you insist on ignoring the fact the dress is IVORY (even Hobbs describes it as ivory)? and looks like a wedding dress?
It's not the "floral" part the issue, all the dresses attached are floral but clearly not wedding gown... 
(they could be, but so unusual it's ok if the guests wear that colour unless told otherwise) Floral wedding dresses are not unusual or rare.
When you can choose all the colours of the rainbow, prints and designs, deciding on an ivory/white/cream/champagne for a wedding where you don't even know the bride... it's just ridiculous. It's not a good look for the guest, that's the point.
I can't understand why, instead of something similar but NOT ivory, and having people commenting on how cute or good you look, anyone would chose something that make them roll their eyes at you. 🤷 Weird.