[throwaway462910]

I've seen the argument before that humans find flowers pretty because they indicate fertile land, where there are flowers there will be animals, etc. Impossible to really know, I suppose.

[yen223]

Anyone who's done any gardening would find that fertilizer - both natural and otherwise - do not smell pleasant.

[yunohn]

Fertile land exists naturally without the manual addition of manure fertiliser.

[JoeAltmaier]

...and smells much the same!

[melagonster]

our monkey brain this mean fruits later, maybe.