This is mostly due to the brand name and size of the manufacturer. Meizu or Xiaomi device get rather an update than a completely new and small manufacturer. In our product selection, we make sure that we only offer high-quality devices that are regularly updated with updates. Xiaomi devices often get weekly updates and adapt pretty quickly to the latest Android version. Also Meizu, Huawei, OnePlus, Asus or LeEco and ZUK offer latest updates.
These can then be installed via OTA (Over The Air), or must be downloaded and then installed with the Updater app.
If your device does not receive an update from the manufacturer directly, please take a look at the community: For example, needrom.com is regularly uploaded by private developers. This also applies to devices whose support has been discontinued. Please note, however, the compatibility with your device.