An important reason to upgrade is the support for SQL Server. Once the mainstream support for SQL Server ends, there will be no more service packs and cumulative updates bringing new features to the old versions.
As you can see from the following table, just three SQL Server versions are supported as of now (Fall 2017). And those are SQL Server 2014, SQL Server 2016, and the current SQL Server 2017:
| SQL Server version | Release date | End of mainstream support |
| SQL Server 2000 | Nov 2000 | 4/8/2008 |
| SQL Server 2005 | Jan 2006 | 4/12/2011 |
| SQL Server 2008 | Nov 2008 | 1/14/2014 |
| SQL Server 2008 R2 | Jul 2010 | 1/14/2014 |
| SQL Server 2012 | May 2012 | 7/11/2017 |
| SQL Server 2014 | June 2014 | 7/9/2019 |
| SQL Server 2016 | June 2016 | 10/12/2021 |
| SQL Server 2017 | Sept 2017 | 10/11/2022 |
Although many of the older versions are not supported anymore, it does not mean those are not...
