Why does the AppleTV App for Amazon FireTV restrict our viewing Movies on AppleTV ?

Apparently Amazon FireTV Prime restricts some viewers of AppleTV+ for FireTV App without adequate warning before users like us signup for AppleTV+... When we tried to view some Christmas movies on AppleTV+ after signup & login, a popup screen appeared claiming these movies were not available for free through any Channels we had subscribed - including the AppleTV+ for FireTV Prime App that we are trying out for the first time. Is AppleTV+ considered a separate channel on Amazon FireTV because Amazon FireTV Prime requires a separate AppleTV+ Channel App to be installed?

It seems to me that Amazon FireTV Prime is trying to squeeze FireTV users like me for more money by restricting our use of AppleTV+ unless we pay Amazon for movies that are free through AppleTV+. I can watch "Elf" and "Home Alone" on FireTV if I pay Amazon an additional $3 - $5 per movie or else when I pay additional subscription fees when I signup for some FireTV Channels other than AppleTV+.

During 12/2020, we signed up for a 7-day trial with AppleTV+ for FireTV App, when we successfully:

1.) installed the AppleTV+ App on our LG SmartTV with no problem,

2.) created our AppleTV ID user name/password, and

3.) logged into our AppleTV+ account through Amazon FireTV Prime.

We can now view AppleTV+ movies made solely for Apple with no problem. However, AppleTV+ prevents us from viewing some Christmas full movies such as "Elf" and "Home Alone" that are listed and currently available for free through AppleTV+. When we tried to view these movies, an AppleTV+ screen appeared claiming these movies are not available for free through any Channels we had subscribed - including the AppleTV+ FireTV App that we are trying out for the first time.

I realize that a work-around for this is if we purchase a separate AppleTV desktop box that grants us full access to all Apple material, including all movies on AppleTV+. However, I don't want the additional expenses and hassles of running separate set-top boxes for Amazon FireTV, AppleTV+, and other providers such as Hulu.

Why does AppleTV+ restict our viewing AppleTV+ movies through Amazon FireTV, which are apparently available to most other AppleTV+ Users with no such restrictions?

Will our AppleTV+ account be granted full access and viewing to movies such as "Elf" and "Home Alone" through the AppleTV+ App and Amazon FireTV Prime after we commit to monthly AppleTV+ billing after the trial period expires?

Your comments and suggestions are welcome!