Planned obsolescence really isn't as big of a thing as people think it is. The problem is that people want the newest shiny thing, and they don't want to pay premium prices for something that'll last a long time.

So, manufacturers will use parts that are less durable to fit a price point. It's kinda like server hardware vs consumer hardware.

Now, development has even less to do with planned obsolescence. Development is expensive, and if only 1% of your users is using V8 while 99% are on v12, it doesn't make sense to keep supporting V8.

This is even a thing with open source software. For example, even though RHEL7 doesn't hit EOL until June, many software vendors have already stop providing updates (curl, for example).