Why do manufacturers not recommend a fuel additive?

I have worked with Jaguar, Landrover, Volkswagen, Jeep, lotus , seat and Chrysler . I have also tested Redex, liqui molly, Diesel blast and mannol. Why are these not recommended ? Products featured are https://amzn.to/41UJSX8 https://amzn.to/4fwgKss https://amzn.to/4iW6JYA Join this channel to get access to perks:    / @glchow