It’s not senseless at all. The costumes made sense in the originals because they were already intelligent apes. These movies are about normal apes slowly becoming intelligent over the course of 3 movies (and though they’re basically intelligent by movie 2, many apes carry over across all 3 films, so suddenly turning Caesar, Maurice, and Rocket from CGI into men in costumes would be jarring) - a person in a costume would look too human to properly sell it. And the motion capture is so well done - I can’t see anyone turning in a performance like Serkis did as Caesar under a costume and heavy makeup.
Give the movies a shot. They’re better than you think, especially the second and third.