"Seasonality" is a response to changes in environmental cues such as light, temp. and water. Every plant species responds to these cues, although the response may not noticably affect reproductive physiology. The rhyme and reason has been worked out for most economically important species (do a key word search with the species name and terms like flower initiation photoperiod etc.). Some of the ones you mention as not being seasonal actually are in most climes. For example, coffee is a short day plant, flowering primarily when the daylength is

For what ever its worth: I was just over on the Big Island and the tour guide at the plantation said the coffee bean season is generally August to December. Looked like they would be gleaning those bushes well into January.
LaurieBee