This is exactly the kind of gene you wouldn't want to spread "horizontally" on its own, just like antibiotic resistance among bacteria.
On the other hand, it hasn't, so far. It does exist in nature, and still doesn't pop up anywhere.
Plants also haven't evolved this functionality on their own. There are evolutionary drawbacks to uncontrolled growth, and most plants have their growth "tuned" well below what would be theoretically possible given their light and nutrient conditions.
The problem is that if we introduce it, it might take a while for those evolutionary pressures to show up. Uncontrolled growth isn't an immediate pressure, it kicks in after the damage has already been done.
On the other hand, it hasn't, so far. It does exist in nature, and still doesn't pop up anywhere.
Plants also haven't evolved this functionality on their own. There are evolutionary drawbacks to uncontrolled growth, and most plants have their growth "tuned" well below what would be theoretically possible given their light and nutrient conditions.