Apps are instructions to the OS. New apps may use new features of a new OS, which aren't available (or work differently) in the older OS. So it's unlikely that a newer version of Maps would work on an older OS.
Even if the OS-bundled apps were available separate on the App Store, the Store won't let you download a version that requires a newer OS.
The notion that Apple deliberately makes older computers (or phones) run slower on new OSes to encourage hardware sales is a lovely conspiracy theory, but not borne out by evidence.
Firstly, it's in Apple's interest to have as many people as possible running the latest OS. A fragmented user base is not attractive to application developers, and having lots of third-party apps available is a major selling point for the platform to users.
Second, Apple makes more money from selling services than Macs. So, if you're paying for Apple Music, TV, iCloud Drive, App Store apps, then Apple is doing very nicely from you.
Making devices appear to be slow is not in Apple's interest, because it reflects badly on the experience of using an Apple device. If your Mac is running slow, you might decide to move to Windows or Linux instead.
Admittedly, to some extent, new OSes (and the apps that run on it) will want to use the increased computing power of newer hardware, so older devices may eventually struggle somewhat.
But at the same time, Apple is primarily focused on giving mobile devices a long battery life, and this is achieved in part by efficiency of operation.
Some older devices are deliberately excluded from installing new OSes because the 'user experience' isn't good enough. Apple spends a lot of time and effort to try to make new OSes run on older devices; and only when they can't cope are they removed from support.
The support lifespan for Apple's phones is way ahead of Android devices. If Apple wanted to get people buying new phones, then they could just reduce the support lifespan.
The only time they have throttled devices is on phones with failing batteries, in order to avoid the phone switching off because the battery can't give maximum power anymore. Again, from the user experience perspective, having a phone that randomly switches off is worse than one that can't use full power.