This is all about chemistry and genetics. But nothing on 'why roses smell nice'. It's really a puzzle. Why on earth should Homo Sapiens consider a rose's smell to be 'nice'? Dogs like roses' smell about the same as shit. They don't give a damn. Further, why are rainbows pretty? Why is a waterfall inspiring? And on and on. You have to have some kind of special model to explain this, I think. Something beyond simple re…
Not all rose types smell as nice as others. There are countless types, all bred for specific characteristics over hundreds of years. If one such characteristic is pleasant smell (and why would it not be), then the answer is obvious. By and large, roses smell nice because human bred them to.
That theory seems unlikely to me since wild roses smell good.
I would say that the modern roses that don't smell good have instead lost their smell because they were selected on other criteria.