[xandrius]

I guess because such a tool starts with you having to input a ton of data before being useful. Either people don't do that or if they are willing then the platform would be getting lots of valuable data and wants to keep you feeding it to increase their trove of data before selling off to Amazon or Google.

[Hendrikto]

I already rated hundreds of movies and TV shows on IMDB, for example. This could be used as a basis.