Because it's more than 2 years old. Samsung major android updates now has 2 years life span. You might still receive monthly security updates. Thanks and enjoy your phone
Will my Galaxy smartphone or tablet get Android 10?
Your Galaxy smartphone or tablet is likely to get Android 10 if it came with Android 8.0 Oreo out of the box. That’s because Samsung offers two major Android OS updates to most of its devices, which means that any Galaxy phone or tablet that was launched with Android 7.0 Nougat or earlier will not be eligible to receive Android 10. That puts flagships like the Galaxy S8 and the Galaxy Note 8 out of the running, even though they may be fully capable of running Android 10. The same goes for any Galaxy device launched before 2018, as it was only last year that Samsung started releasing phones with Android Oreo out of the box.
