Google gave the Mobe OEMs what they wanted, a fully customisable OS they could use free of charge and left them to support the OS and apply any patches. Google's only aim was to sell as many apps and stuff it could through the Play store, steal as much user info as possible and if possible destroy MS along the way. The manufactures only interest was/is selling as many Phones as possible.
Android was never designed to be patched, it is basically similar in design to Windows 95 in this respect and here in lies the problem and the difference to the way Windows 10 works now, which is supported for patching on a much larger range of hardware than Android runs on.
The big thing that is ignored here is that drivers are provided by the component manufactures not the seller of the kit, this is the main blocker for OS upgrades (always has been for Windows as well, go on the Dell website and try and find some Windows 10 drivers for kit that was sold with XP ro even 7, some of their specialist hardware be missing).
With XP, to a certain extent, and Windows 8 and 10, to quite a large extent, MS wrote drivers for a lot of kit that the component and peripheral manufactures could not be bothered with, to ease the migration of users. No one wants to upgrade an OS only to find they need to buy a new printer (remember Windows 2000?).
MS spent most of the 90s and 00s being battered into putting effort in to supporting end users and looking after them, they are not perfect, and let down by the big OEMs, but are a damn sight better than Google who no one seems to care about how bad they really are towards their customers and how they abuse their dominant position in the market.
GDPR will could have an interesting effect on this relationship as Google could find its core business badly hampered and subject to much litgation.