They're not, unless you're willing to pay extra for them to be.
Netflix is not preservable, DVDs are.
Spotify is not preservable, CDs/MP3s are.
Most of the stuff we watch/listen to is on non-preservable media, and for the most part, we don't care.
If you really love a certain movie or song/album, you will buy it separately. Why not the same with games?
They absolutely used to be preservable until an enormous technological effort was made to make them non-preservable. The amount of people curating their CD (or later MP3) collections showed they cared very much.
> If you really love a certain movie or song/album, you will buy it separately. Why not the same with games?
Because it's not clear at all that this option would still exist. From a publisher's perspective, it's vastly preferable to just sell access to your game and keep the actual binary under wraps. So if there is a way how they could realistically do that, I don't think there will be much motivation to also offer the game as standalone software.
Or, to be more precise, you'll able to "buy" the game alright, but what you're buying is just access to the game on a streaming service, not an actual copy.
Which, to be fair, is also the desired effect of something like Steam. If Valve turns off your account, you lose access to all the games you've bought.
The last resort of tricking the DRM to retain access to the stuff you "own" is only possible due to the technical limitations that mandate distribution of the files to a user's local system. I'm sure publishers would love to be able to just stream blobs, making this type of thing much more difficult.
Due to this I'm actually kind of hoping for this service to fail to catch on.
With Stadia, you pay once monthly, and then you pay for the game on top of that cost. The same price you'd pay if you bought the game for any other platform, which also has the benefit of letting you own the game (physical copies, files downloaded to hardware you own).
You're comparing apples to oranges.
What the platform promises is to match the ease of use of YouTube or Netflix. If it can actually deliver on that, I'm sure we'll see a lot of different business takes on the same technology. As someone who started gaming on an Atari and still maintains a top-of-the-line PC, I see a streaming model as inevitable since games need to compete with the Netflixes of the world for your attention. As a new dad, the barrier (timewise) to actually playing something these days is prohibitive, so Netflix wins by default for me when I have an hour.