>>12662992It's because the flower is pretty much an extension of the Pokemon, much like Dwebbble's shell home, Farfetch'd's leek, Spoink's pearl, Timburr, Gurdurr, and Conkeldurr's weaponry, etc. It is as much an important aspect to that Pokemon and its background as anything else is.
The info text in CoroCoro stated that it finds a flower after being born and stays with it for life. Perhaps there's some kind of symbiotic relationship that the two have?
