It's because just terminating a goroutine isn't safe with respect to I/O and defer chains.

I think Go has the internal plumbing to theoretically support this, though it might require inserting checks more often. Another way would be to make contexts first-class and automatically insert context checks even when not done (e.g. selects). And also all I/O has to be cancellable.

I suspect Go's designers prefers the current way in which cancellation is explicit.