It’s a deliberate provocation, he certainly anticipated exactly this sort of response.

In a sense he is exploiting a lack of rules that would prevent a piece from starting with this long of a rest.

In other words, he is hacking the process.

To be fair, while the piece is a deliberate provocation, like some of his others, the rest wasn’t imagined by Cage to take 17 months, that’s just an artifact of someone else’s decision to play the piece for 639 years. In typical performances while Cage was alive, the opening rest wasn’t more than a few seconds.