After Mackbook M1 purchase received an Apple TV+ free for a year, but literally nothing is free there, why it is like that?

The free subscription is for Apple TV+ (note the "+"); that is Apple's streaming service. It does not include other content that can be purchased on Apple TV.

To see what is included in Apple TV+, see: Apple TV+ - Apple

The current selection would be 20 movies and around 42 series/specials, with more added each month. It isn't meant as a competitor to Netflix, but to be honest that costs a lot more (in Canada Apple's costs $5.99, while Netflix costs $15 and $19 for the HD and 4K plans respectively..Europe's price for this service is 4.99). Also, Netflix has been around and had a chance to build up it's library, during it's first few years it didn't have much either.

If you are looking outside of Apple's service then those are prices for rental or purchase, which are set by the studios and quite comparable between digital storefronts. Cinema and rentals would be more equivalent as they are a fee for a one time viewing, home rentals will only cost more if it's a film that is still in theatres. Purchases will always cost more as you are now owning that title.

Bottom line. If you were getting it for free then you really have nothing to lose and can simply stop it before you are billed.

you can let them know using their feedback channel Feedback - Apple TV App - Apple