The reality of creating your own personal video library:
1. The formats you purchase are proprietary. Meaning that should the vendor (such as Apple, Amazon, or whoever) decide that they want to switch to a newer format in the future, all your old purchases may no longer play on newer hardware/software. This is strictly speaking to content you download to preserve locally. Content stored on their servers is updated to the newer formats if possible, the only caveat is that they can lose licensing privileges from the owner or choose to remove it to make room for newer titles instead. So there is no guarantee that the title will remain available forever.
2. The files are large and consume huge amounts of disk space. This means that you are required to maintain a storage device with enough terabytes to store the content. 4TBs is the minimum to start with if you wish to create a video library. You will need to expand it as your library grows. These devices require a backup as well should the primary storage device fail (they can and do). This can become a substantial investment especially considering the fact that you will need to update the content yourself to the newer formats (i.e. re-purchase them again).
So looking at a subscription fee versus all this and you will see that the subscription is actually simpler and less expensive. Say you love the Marvel franchise or Star Trek... for a mere $5-$8, you have 30 days access to pretty much the entire catalog of said movies when you have an itch to watch them again. Ask yourself how often you actually want to watch this content again. Most people with video libraries watch maybe 10% of the stuff they have saved for personal use. The rest of it just eats up space, never to be viewed again.
Generally speaking, unless you are into watching the obscure, odds are pretty good the stuff you want to watch is available via a streaming service. If you are frugal and are into binge watching, you can hop from one streaming service to another to get your fix as seasons are completed. For example, say you are a Star Trek fan... Paramount+ would be subscribed to once all the seasons of the shows you wish to watch have aired for the season. Picard season 2 ends in May, Discovery's latest season just ended a short time ago... that means if you wait until May, for a single subscription fee, you can watch all of the new content for the course of the month. Granted there will always be cross-overs, but in general, you can hop from service to service without actually subscribing to more than one at a time. What you don't want to do is subscribe to multiple services at the same time. That's too much overlap and you actually end up spending way more in the long run.
The reality is, streaming services are replacing traditional movie going and TV. The days of owning a video library are numbered in that the studios are less and less inclined to sell you the right to own it. DVDs are disappearing at a rapid rate. It won't be much longer before all you are offered is the option to stream it or rent it, never the option to own it. Technology is changing rapidly, the home video library is becoming a thing of the past, much like CDs and VHS.
