I agree that he's likely to opt out, but that still doesn't explain why he would sign an extension without hitting the market. He's holding the cards here. Signing an extension negates his leverage. If he's hurt, he's still got the option years to regroup. If he's healthy, he opts out and takes advantage of the market. He's in his prime, so an extension is exceedingly unlikely. Especially with Boras as his agent. He'll shop the market.
The trend has been to sign short term high AAV contracts of late. Signing a 28 year old at $35M plus for 7-10 years goes against that. Especially for a guy that gets dinged up as Correa does.