The Windows 10 update model
Windows 10 is used mainly on PCs.
Microsoft sells Windows 10 licenses. You buy a license, and then you can install Windows 10 on your PC. Then you can get security updates directly from Microsoft. Microsoft promises that they will continue to provide security updates for Windows 10 for one decade after it was first released.
Windows 10 includes so many drivers that it works on many PC models.
The Android update model
Android is used on cellphones, tablets, and other devices. Tablets have no moving parts, so they can last longer than laptops.
Google distributes Android to tablet makers. Tablet makers create tablets. They combine Android with a set of drivers to create a firmware image custom-made for a particular tablet model. They then install this firmware image onto the tablet model. Finally, they sell the tablet model to individuals and corporations.
Each Android firmware image includes enough drivers to work on the tablet model it was designed for. Experts advise that you shouldn't bother trying to install it on any other tablet model.
The problem with the Android update model
You can't get a universal Android firmware image from Google. Instead, you have to wait for your tablet manufacturer to add drivers to it, in order so that it will work on your tablet model. And your tablet manufacturer might never do so.
Numerous tablet users are running old insecure Android versions, and they're running these Android versions on devices which the tablet manufacturer has stopped supporting. Therefore, there's no easy way for the users to install patches which fix the vulnerabilities.
Why doesn't Google distribute Android firmware images with lots of included drivers, which will work on lots of Android devices? Google could include the latest security fixes in these firmware images. If Google did this, maybe there would be fewer vulnerable Android devices out there.