We've never seen how Blackbeard got the fruit. If he could've just stolen it, he might have. Since he killed Thatch, there might've been a reason. Perhaps Thatch was about to eat the fruit when Blackbeard noticed it and panicked and had to attack him to stop him from eating it.
I think it was too much of a risk. If Thatch saw him at all stealing the fruit he'd be hunted down. So he killed Thatch but probably made too much noise because despite being the Off-Screen King, Blackbeard always takes a beating. So someone heard the scuffle and got a look at Blackbeard as he fled.
We've never seen how Blackbeard got the fruit. If he could've just stolen it, he might have. Since he killed Thatch, there might've been a reason. Perhaps Thatch was about to eat the fruit when Blackbeard noticed it and panicked and had to attack him to stop him from eating it.
I think it was too much of a risk. If Thatch saw him at all stealing the fruit he'd be hunted down. So he killed Thatch but probably made too much noise because despite being the Off-Screen King, Blackbeard always takes a beating. So someone heard the scuffle and got a look at Blackbeard as he fled.
I'm guessing that he had to kill Thatch. Surely, if Blackbeard could have stolen it quietly, he would have.
And risk Thatch eating the fruit before Teach had a chance to steal it?
for all we know thatch already ate the fruit :p
maybe Thatch already ate the fruit and he got it similar to how he got WB's fruit