Take a look at why the Windows Phone failed.
Much like BlackBerry, Microsoft too doubted the iPhone's potential success after its debut in 2007, saying that it won't appeal to business people as it can't be a good email device as there is no keyboard.
Furthermore, Apple was the first smartphone (and business phone) that was exclusively made by one manufacturer for both the hardware and software, which gave Apple a huge advantage over quality control and user experience. But Microsoft, yet again, thought it was going to fail as it was the most expensive phone in the world at the time.
during this time, Microsoft was already years ahead in mobile phone technology experience as they had already been making operating systems for PDA's. However, another company was on the rise in the mobile phone game and that was Google with their operating system, Android. Andriod was after every mobile phone manufacture they could get their hands on to provide operating systems for.
Microsoft, however, took a completely different approach and partnered with the dying phone brand Nokia, which they had hoped to take Apple's approach by developing the hardware and software for a new range of phone. However, it was poorly received and third-party developers didn't even bother making apps for Microsoft, but rather for Android and Apple.
Take a look at the video below by YouTube channel, Business Casual, on Why Windows Phone Failed – And How They Could Have Saved It.