Live-action adaptations provide more content for fans of a series
Fans of anime, or any kind of entertainment, love to consume more and more of it. Whether one's favorite anime is part of the hottest current trend, or one of the classics from long ago, fans are hungry to see more of their favorites. In live-action adaptations, they have more content for them to watch and enjoy. It may be the same characters and story, but fans nevertheless enjoy seeing those characters and story that they fell in love with in the first place. And even if many things stay the same, there are certain differences in a live-action adaptation that enrich the experience. One can see different takes on character, different directorial choices, even alternate paths for the plot. The value of an adaptation is that it can tell an old story in a new way. Live-action adaptations show how to express the eccentricities and nuances of anime in a medium more akin to real life. Bringing old favorites back to give to the fans will almost certainly delight them. It is especially effective with ways to keep the story fresh with new elements sprinkled in. When executed well, live-action adaptations can provide great entertainment to fans of the original source material. This explains the number of adaptations that appear in the media today.
New material is useless if the material is bad. Live-action adaptations of anime have long since been terrible. Movies like "Dragonball Evolution" (one word? Really?) and the Netflix "Death Note" movie have been slammed by critics and fans alike. Creative reinterpretations can often have disastrous results. Whether it's whitewashed casting, costumes that just don't work in real life, or over-exaggerated acting and effects, there are a lot of aspects of anime that just don't translate well into live-action. Animation as an artistic medium allows for fantastical stories to be told and imaginative things to be shown which can't be reproduced in live-action filmmaking. Putting something that is fantasy into a more realistic medium takes away the magic and charm which made fans appreciate the anime in the first place. It's best to let animation stay in the realm of animation.