Because grey lotus is designed to be rare, and it need at some point to harvest chests in the arena, with this change you just need 1 seed to start infinite production (providing compost).
All other things you mentioned are not designed to be rare and powerful, they aren’t. All things you mentioned you need large quantities of them, wich is not true for ALL plants.
With the possible exception of the new fishes: they are OP but still, they require at least to check frequently the new fishtraps, because if not, the very low rate of capturing them makes them decay and so if you let the fishtraps unchecked for days you’ll don’t find any of them.
All lotuses for example in theory are designed to be rare, in reality only grey lotus it’s really rare but it’s powerful.
A planter do not even work this way, what you produce do not decay, you start growing with just one seed, the plants will stacks (now I think is 1 seed = 10 plant) with this suggestion you’ll produce also seeds, continuing the production in (potentially) exponential way if you do not produce only 1 seed from 1 seed, until the compost will be finished or the planter full.
So, starting from one seed, you’ll able to store hundreds of grey lotus.
It’s not an unbalancing change, but warpaints and potions based on grey lotus are used only for good reasons, because they require a rare ingredient, if you implement this they’ll become each-time-I’m-outside-my-home standard equipment.
Are you sure the game balance will not affected by this change ? I’m not.
That’s what I’m saying with “abusable”.