Starting from Android 6, it's easy to check if the device is up-to-date from an Android point of view: in "About phone", you have an "Android security patch level" section which should be match the current month.
Yes indeed - the downside of this is that it's hard to gather this information together in a way that lets you show people "which devices" are still maintained.
It is much better for users to know if they are on the latest build. Sadly though for (most/many?) devices, the answer is "it's not", and there's nothing they can really do about it, either due to OEM latency in releasing updates, or the OEM having abandoned their phone.
Samsung [1] and LG [2] pretty much say on their own websites that only certain phones will get updates promptly (or at all) - consider their full product ranges and the cheaper devices not even listed!
It is much better for users to know if they are on the latest build. Sadly though for (most/many?) devices, the answer is "it's not", and there's nothing they can really do about it, either due to OEM latency in releasing updates, or the OEM having abandoned their phone.
Samsung [1] and LG [2] pretty much say on their own websites that only certain phones will get updates promptly (or at all) - consider their full product ranges and the cheaper devices not even listed!
[1] http://security.samsungmobile.com/introsm.html
[2] https://lgsecurity.lge.com/security_updates.html > Depending on regions and carriers, updates may be released monthly, quarterly or irregularly.