SMSes don't have a standard way to insert line breaks
Unfortunately technical people often can't seem to get simple things right. Unbelievable but not so unbelievable if you look at the history of HTML and how many many websites to this day are generating "bad" HTML.
FROM Technical Challenges in Content Delivery to Mobile Devices | Mobile Muse:
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Our first surprise came when we discovered that even a "tried-and-true" standard like SMS - that world-wide delivers billions of messages monthly - is not so much a standard as a guideline. Something as simple as inserting line-breaks in content is not, in fact, specified in the protocol as a requirement and it is often not implemented at all by certain platforms. This makes it very difficult to deliver even the simplest "structured content" (i.e. a list) in an easily understandable fashion.
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