WhatsApp was bought because it was popular in India and Brazil, markets that have historically been weaker for Facebook Messenger. Together, they ensured that Facebook would get a nigh-insurmountable lead in marketshare over Google in the messaging space [1].
Twitter in neither a threat to anyone, nor a strong candidate for a defensive purchase [2][3][4]. The two companies are hardly comparable.
Yeah but people don't like being monetized. If someone has to pay to get a tweet in front of you then it's probably because nobody would bother to spread that information for free, so chances are any sponsored tweet has low value to the viewer. Conversely if you can have huge reach by paying then the (slim) value of social proof becomes meaningless because you're not really popular, you just bought the digital equivalent of a billboard in an attempt to seem popular. Adding too much money lowers the overall value proposition.
Being bought doesn't mean it had the ability to turn a profit. I don't think WhatsApp would have been able to do this on its own at the donation-ware level prices they were asking for ($0.99/year).
Twitter in neither a threat to anyone, nor a strong candidate for a defensive purchase [2][3][4]. The two companies are hardly comparable.
[1] https://news.ycombinator.com/item?id=13465483 [2] https://news.ycombinator.com/item?id=11914620 [3] https://news.ycombinator.com/item?id=12420732 [4] https://news.ycombinator.com/item?id=12083975