When you are looking for rainwear, you need it to be protective but it should be breathable as well.
There is a fine balance of outerwear to get breathable but yet waterproof at the same time. However, when you are out in the rain, you want to keep yourself completely dry. This is especially important when the weather is a bit on the cooler side. It could be dangerous to be out in the rain without proper protection.
Rainwear is also perfect for those fishing trips that you are going to be in or near water.