Why microsoft Bought Nokia

Abandoning Windows Phone Is Not An Option
It is true that Windows Phone operating system has failed to achieve traction comparable to Apple iOS or Google‘s Android.  Given that mobile devices will dominate the foreseeable future, Microsoft has no choice but to change strategies and try again until it succeeds.
Nokia sells over 80% of Windows phones.  For this reason, it makes sense for Microsoft to take control of this strategic asset in its quest to become a services and devices company.
Eliminating Duplication
Right now there is a lot of duplication between Nokia and Microsoft.  Nokia is about to introduce a tablet to compete with Surface.  Microsoft has been readying a Windows phone of its own.  All of this duplication will be avoided after Nokia device business becomes part of Microsoft.
Carrier Relationships
In the mobile phone business, relationships with phone carriers across the globe are very important.  Microsoft does not have many such relationships.  On the other hand, Nokia has such relationships, on par with Apple and Samsung and in many emerging markets better than Apple.
Logistics, Manufacturing And Supply Chain
To be successful in the mobile business on a global scale, extensive supply chain, logistics and distribution networks are required. Nokia already is preeminent in these areas whereas Microsoft is in its infancy.  Nokia also brings substantial manufacturing capabilities. Microsoft may be able to leverage the manufacturing capabilities to produce further differentiation from Apple which contracts out most of its manufacturing.
Talent Acquisition
Nokia is well known for its hardware engineering talent.  Duplicating this talent is not an easy task.  Microsoft will be able to leverage this talent not only on phones but on a range of devices.
Nokia CEO Stephen Elop went from Microsoft to Nokia to become its CEO.  Now he is coming back to Microsoft.  Since Steve Ballmer is retiring, Elop is a top candidate to replace Ballmer.  After all, he has experience running a global organization with thousands of employees, expertise in mobile and familiarity with Microsoft.
Use Of Overseas Cash
The transaction is tax efficient in that Microsoft will be able to use its overseas cash to pay for the transaction and mostly avoid U. S. corporate tax on this cash.
The next two years are going to be difficult for Microsoft.  The dips in the stock will be buying opportunities for the investors with very long-term horizons.