All Android phones are not created equal.
Good article goes into detail about the machinations involved in getting the latest version of Android onto Android based mobile phones.
Yes ‘Android based’ mobile phones, that’s important because almost all so called Android phones come with an operating system ‘based’ on Google’s Android.
Even new phones often come with an older version of Android because the manufacturer hasn’t modified the base OS to work on the hardware. Or the carrier hasn’t made it’s modifications and given approval for it’s use on their network.
If you want a new Android based phone with the very latest Android operating system then your only real option is to buy an unlocked Nexus direct from Google.
iPhone users don’t have similar problems because Apple is the only source of iOS and the hardware it runs on. All software updates come solely from Apple. The carriers are not involved and iPhone users get the updates as soon as they are released. Guaranteed to work on their particular device irrespective of carrier or geographic location.