For most companies, having two competing products internally does not also prevent you from having two competing products externally. There's no law preventing an outsider from starting a competitor just because you've already got two alternatives.
Whatsapp is a great example - Facebook already had Facebook Messenger, and Facebook Chat, internally. Google had GChat and Hangouts and whatever else they're working on these days. It didn't prevent the outside company with half a dozen employees from eating their lunch.
The parent's point is that because of their core markets in search & social networking, Google and Facebook have the luxury of no major competitors, and so they can afford the internal competition to advance the state of these markets. The market structure came first, not the corporate structure. And if you try that in a market with few barriers to entry (like mobile chat, before everyone had built their network effects), it's just as likely that a competitor outside the company will eat the market, not one inside the company. Probably more likely, since internal projects are hamstrung by things like executive approvals, PR worries, and potential legal issues while startups can just take their product to market and see where the market takes it.
Whatsapp is a great example - Facebook already had Facebook Messenger, and Facebook Chat, internally. Google had GChat and Hangouts and whatever else they're working on these days. It didn't prevent the outside company with half a dozen employees from eating their lunch.
The parent's point is that because of their core markets in search & social networking, Google and Facebook have the luxury of no major competitors, and so they can afford the internal competition to advance the state of these markets. The market structure came first, not the corporate structure. And if you try that in a market with few barriers to entry (like mobile chat, before everyone had built their network effects), it's just as likely that a competitor outside the company will eat the market, not one inside the company. Probably more likely, since internal projects are hamstrung by things like executive approvals, PR worries, and potential legal issues while startups can just take their product to market and see where the market takes it.