According to new figures from analytics company Mixpanel, via MacRumors, iOS 11 is being adopted by users at a slightly slower rate than iOS 10, having been installed on 10.01 percent of devices 1 day after launch. In comparison, iOS 10 was installed on 14.45 percent of devices in the same time period, and iOS 9 on 12.6 percent of devices. iOS 8 was also very similar.
And while this might be somewhat surprising, given the relatively smooth experience of installing iOS 11, as MacRumors notes, people might have initially been a little reticent to download iOS 11 without waiting a little while due to problems experienced in previous years. I know that I definitely waited to make sure that there were no major bugs reported before taking the plunge.
Also, as MacRumors mentions, another factor behind the slightly lower uptake of iOS 11 could be that all 32-bit apps will be disabled once iOS 11 is installed, so people might be wanting to check if they have any such apps that they might rely on before installing the software.
Source: iOS 11 Installed on 10% of Devices 24 Hours After Launch