In my case, I lost access to one of my Google accounts, for no apparent reason, and I have been unable to regain access. The movies I have are actually attached to my other account, but the message seems clear--they can go away at any time with no recourse.
In principle this is true for Amazon, Apple, and other Play competitors. In practice, I haven't heard of such cases, and because their economic model is different, this seems a lot less likely, to me.
More broadly, Google has a track record of discontinuing services, which also makes me nervous.