Why aren’t iPhone text messages at full width?

Why aren't text messages viewed on the iPhone iOS displayed at full width? I can think of several reasons why it would make sense:

• Short messages won't have unnecessary line breaks, long text messages will be easier to read.
• Text messages with an even width and alignment will have an improved sense of vertical and symmetry.
• Contrast of colour and the tails of a message bubble indicate if a text is an incoming or outgoing message.