Prof. SALTY
The Scruffy Professor
I love the passion going into this answer however this is actually a far more smarter and safer move than you think for several reasons. Think of it as a prototype for something bigger.
First off, video game film adaptations. There is a practically a lot of infamy and taboo surrounding video game film adaptations and in this day and age where film studios are milking off of people's nostalgia's, Detective Pikachu is a safer bet because if film studios were to milk off and experiment with the nostalgia of Red and Blue, it might lead to mass disappointment from fans as many fans these days are no stranger of keeping their expectations at extremely high levels out of nostalgia despite the reoccurring trend of bad movie's failing to understand what fans want while at the same time making their own surprises to keep things interesting. Most film studios have a bad habit of not understanding the source material and even then, they have a bad habit of experimenting with video game concepts that are too large for filmmaking. Detective Pikachu is far safer because it's an adaptation of a spin-off and is a great compromise and start for a potential Pokemon film franchise and introducing the concept of the Pokemon World while maintaining that hype and nostalgia from people's childhood memories of Pokemon through a more smaller and less-grandiose story that not many casual Pokemon fans are familiar with and yet won't be as disappointed because they know this isn't Red, Green and Blue. This is Detective Pikachu, based on a spin-off which also leaves for more experimentation to see what works in a video-game film.
The second reason is Nintendo themselves. As reasons mentioned before, the film studios have less chance of messing a Detective Pikachu film as the first live-action Pokemon film then an actual adaptation of the main series games we all know and love and through this they have one chance of slowly earning Nintendo's trust in video game film adaptations which could lead to Nintendo possibly opening their doors full of video game properties to carefully pick film studios creating a series of Nintendo films after over 20 years of Nintendo never trusting a film studio ever again with their video game properties after the disastrous movie known as the Super Mario Bros. movie which is to this day a masterful example of how often western film studios do not understand their audiences that well.
To sum it up. If successful, Detective Pikachu will be a very important movie in cinema and video game history and may determine the possible future of not only a Pokemon Red & Blue movie but a wide array of possible Nintendo film adaptations that could represent the bulk of video-game film adaptations. If it fails, we may never see a Nintendo film adaptation in what I assume the next 10 to 20 years.
While I agree with you to an extent, I think you give movie producers too much credit. Hollywood doesn't seem to realize game adaptions are bad. I think the reason Detective Pikachu was chosen was because the game is a self contained story in an easily adaptable genre. I do think it is an important moment in gaming history but I don't think the studio was looking past the buttload of money they're gonna make.
As for Nintendo being more comfortable with film adaptions, I don't think it's likely. Nintendo are much stricter with their IPs than Gamefreak is with pokemon.