They got too ambitious with the story while refusing to actually "up the stakes."
Back when it was just monster of the week you could forgive every second episode just being townie shit or about the characters just growing up, because that's what the show was, just Steven learning how to use his powers and interacting with his surrogate sisters and the townsfolk with a little hint of lore sprinkled in.
Then they started trying to make the show more serious, intergalactic genocidal space god-beings leading an entire empire across the universe, some ancient war for Earth that constantly haunts the gems and leaves scars all over the planet, etc... They added all this shit, but they still kept the townie shit and the character development episodes and it just ended up feeling like they rushed into plotpoints they didn't want a single thing to do with since every time the plot started to get a bit of tension to it they immediately stopped that particular plotline to go back to SoL stuff; the show felt very schizophrenic with its tone.
Thankfully though the latest episodes actually do seem to finally realize what they want the show to be and are trying to stick to a single tone, though it's a little too early to tell and they may still end it way too quickly, but I'm optimistic.