The green wisps aren't necessary since that rejuvenates itself over time. It could be confusing for those new wizards who don't have pets or gardening as yet.
the health rejuvenates itself also so im confused why there isnt any green wisps
In short it is a way for KI to make money. You don't NEED to buy energy replentishing from the CS (cash shop) but it does make it go faster if you do. IF they did implement this idea then a) they would need to do something else for membership accounts (since membership accounts get 1 energy every 7min) b) there would be no throtal on how fast everyone could get to have multiple epic pets. ATM that is somewhat limited to heavy CS users.
Basically this is like anyother mmo, you have to make choices. Depending on those choices will depend on what you progress faster in. I personally have a very small garden (3 plants up to 5 at one point) and I now have 2 epic pets.