At the time, Instagram had 80 million users, it had no monetization strategy and was profitless[1]. I suppose this made it seem less of an immediate competitive threat to Facebook's business model, especially with the presence of other smaller photo sharing platforms by Google etc.
In 2020, the Wall Street Journal reported that FTC officials in 2012 had concerns about the deal raising antitrust issues. However, they were apprehensive about potentially losing an antitrust case in court if they sued to block the deal.[2] If they would lose then on the merits of trying to enforce the Clayton Act, it would set a precedent that likely could not be undone.
I remember hearing from friends at Facebook that an insider story was FB used VPN and in app IP address tracking to identify that instagram and whatsapp were hitting crazy growth metrics and that's how they knew they needed to buy them at all costs
Onavo, the VPN app-company that was repurposed by facebook for market intelligence, was only acquired in 2013, Instagram was acquired a year earlier in 2012.
But before 2013 there were methods on both iOS and Android for an App to get a list of all OTHER installed apps on the device.
Facebook had the means to know exactly at which rate each app was growing and how many of the users they have to share with it, the facebook app itself was gathering this info.
They could gather enough data to even calculate how much user-attention they lose after each app is installed on a users' device.
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Onavo was then acquired in 2013, right when Apple started to lock-down those app-scanning methods with iOS7.
So it appears that the company was acquired to be able to KEEP doing something they have already been doing before that with the facebook app.
In 2020, the Wall Street Journal reported that FTC officials in 2012 had concerns about the deal raising antitrust issues. However, they were apprehensive about potentially losing an antitrust case in court if they sued to block the deal.[2] If they would lose then on the merits of trying to enforce the Clayton Act, it would set a precedent that likely could not be undone.
[1] https://www.ibtimes.co.uk/facebook-instagram-deal-down-747m-...
[2] https://www.wsj.com/articles/tech-ceos-defend-operations-ahe...