Satya Nadella was named Microsoft CEO February 2014. What was the Microsoft Mobile world like before he started? Well here's an article to remind everyone from January 2014:
Kantar data shows Windows Phone holding 10% sale share in EU5
Basically, Nadella has crushed Microsoft Mobile with bad strategic and tactical decisions. He thought he could drop Windows Mobile OS and devices, but deliver services on Android and iOS that people would use. He was completely and utterly wrong. People are strongly biased to use the services native to OS.
Nadella's complete failure on "Mobile First":
Microsoft?s Office Being Dominated by Google Productivity Apps on Mobile? - WinBuzzer
So not only did Nadella kill Microsoft Mobile OS and devices, his strategy is killing Microsoft in Mobile services too.
PC's continue to be on the decline, while the area Nadella abandoned (phones) are on still on the rise. Phones are the consumer IT of the present and future. Running to the Enterprise will only protect him until the new Android/Google users become decision makers in companies. Once that generation is in control of the enterprise decisions, Microsoft will be done.
In other words, if leaders of a company use Android phones, Chrome, Gmail, Google, etc. for their personal devices, they will be strongly biased to chose Google services and products (stuff they are comfortable with) for the Enterprises they run. IBM already learned this lesson decision makers chose Microsoft products (stuff they used at home), but Microsoft (and specifically Nadella) didn't learn from IBM's painful decline from relevance.
Look, everyone loved Nadella when he started, but every new CEO gets a honeymoon period, and that takes the stocks to unreasonable heights based on speculation of future greatness. Remember when Mayer took over at Yahoo? However, it is clear to see that Nadella has already made too many mistakes. The stock is starting to slide, Nadella abandoned Mobile, while PC's decline. How long before Google fans become enterprise decision makers, and Microsoft fails in Cloud and Enterprise too? It will take 5-10 years for Microsoft to recover from his 2 year term, and that would be if they fired him today.