The controller wants to defeat the Siege, because once the Siege's last defense counter is removed, it is exiled, and its controller gets to play its reverse face for free
P/T Number 234 Language English Legal Formats Commander, Historic, Legacy, Modern, Vintage Not Legal Formats Alchemy, Brawl, Competitive Brawl, Pauper, Pioneer, Standard, Timeless Rulings (6/16/2023) Damage dealt to creatures remains on those creatures until the cleanup step or until an effect removes that damage
With buylists you can get your money back within a week, with eBay you can get it back instantly assuming you find a buyer for the card )
Green has a ton of synergy with +1/+1 counters, with cards ranging from The Great Henge to Benevolent Hydra bolstering this strategy in recent years
When it dies, it leaves behind two 3/3 tokens, one with lifelink and one with deathtouch