> The question is: why would a smartphone be required, to watch a local game?

It's not. You can still buy physical tickets in person to watch a local game.

This is a requirement specifically for a season pass. If you don't want a season pass, you can still buy individual tickets.

It is not required to watch a game. At least not unless you are not using it as some kind of vision aid — although even then there are likely reasonable alternatives.

It is required to satisfy the desires of a vendor wanting to sell something. They make a smartphone a part of satisfying their desires because it makes their life a whole lot simpler. Same reason they won't give you season tickets in exchange for 12,000 bushels of wheat. They could, but why would they? If you don't want to play ball, so to speak, they are happy to sell their product to someone else who will.