Counterspell has a long history as the cleanest possible answer to anything on the stack, and its Modern printing gave blue decks a nostalgic yet powerful option. In Modern it mainly shows up in more traditional control shells that want hard permission rather than soft counters. The double blue cost pushes it toward slower, heavier blue decks that can reliably leave two mana up. Its iconic status and broad utility keep it in the conversation whenever players tune blue control lists.