Consider that if they couldn’t protect their work, they never would have invested the money into making these and offering them for sale to begin with.
I understand why some might find it unpleasant, but the fact that these exist at all is a testament to why such protections are available.
That's a massive assumption. Plenty of other plants are sold every single day that aren't patented. There's zero reason to assume that they couldn't make a very nice profit on these plants without a patent. Just like every single florist in the country does.
I don’t understand what you’re trying to argue, but the patent laws aren’t designed to patent generic, pre-existing plants like generic watermelon.
This is not a natural plant though.
Edit: it also seems that nontrivial engineering work was required to improve bioluminescence. It was not as simple as straightforwardly splicing in a few genes from a mushroom.