Why are mid-2009 15" MacBookPros excluded from downloading OS X Sierra?

macOS Sierra requires any of the following Mac models and versions of macOS. It also requires at least 2GB of memory and 8.8GB of storage space. To find your model, memory, storage, and macOS version, choose About This Mac from the Apple () menu.

• iMac models from late 2009 or later
• MacBook models from late 2009 or later
• MacBook Pro models from mid 2010 or later
• MacBook Air models from late 2010 or later
• Mac mini models from mid 2010 or later
• Mac Pro models from mid 2010 or later

No mid-2009 models can install Sierra because they do not have the compatible hardware or chipsets necessary to run that operating system.

To check the model number hold down the option/alt key, go to the Apple menu and select System Information.

macOS 10.12/10.13 (Sierra/High Sierra) require one of the following Macs:

MacBook (Late 2009 or later) Model 6.1 and higher

MacBook Pro (Mid 2010 or later) Model 6.2 and higher

If you get creative with your internet search criteria you will find a way of enabling the upgrade on your Mac.