I hate to be the broken record but it is all about costs and time from server engineers, dbas, and application folks for the huge amount of hours for an upgrade. Every release of SQL Server I have heard this is the best thing... will make things run faster....  2000.. 2005(introduction of 64 bit)  2008R2... 2014 (new cardinality)...2016..2017...  In our upgrades from 2008R2 to 2014 I saw no noticeable improvement in throughput.  Like I have stated before if I were to give our CIO a cost of what it would take to upgrade everything he would flip.   Not to mention the number of hours involved.   Don't get me wrong... I am sure these advances are very good.  However, one has to remember that most systems are not running slow... or will not really experience a great improvement as they are low end systems that just need a database to store data in.  I am sure the mid to high end systems people will be thrilled with the improvements.  However, the costs of licensing will be much higher and the application testing time will even be more significant for larger systems.