Trigger tried to Triggerfy it.
Trigger and A-1 made a pretty bog standard mecha show trying to ape some themes from popular shows. Throw in a layer of romance over the top and some LE WACKY characters with more than a sentence written about them and people loved it.
Then they didn't know how to end it. The "Threat" wasn't really presented until episode 15 with Klaxohime, we finally had a "VILLAIN" to worry about. Except she wasn't the villain, APE was, which was obvious, but too obvious.
Trying to manage all of the characters with convincing arcs came off poorly when they realized that 24-episodes wasn't enough. So they started to appeal to what people liked, they liked MitsuKoko, so they pushed that. They liked Hiro and Zero Two, they kept pushing that. Everything else got put to the side, but not dealt with.
Then they didn't know how to wrap it up, so things started to get resolved quickly. Klaxohime? Dead(ish), Franxx? Dead. APE? Dead/Soul Eaten.
VIRM was something pulled out of their ass to justify a massive threat. It wasn't "Foreshadowed" very well at all, it just HAPPENED. They just HAPPENED to be budget Anti-Spirals / Angels because that's what Trigger does. >tl;dr>Show was too ambitious and Trigger/A-1 realized no one likes Trigger unless le wacky