I mentioned that a a few posts back as well. This release strategy is definitely costing them now since the show is so weird and such a slow burn. It basically did a little bit of what TLJ did and they subverted the expectations (those that don't pay close attention to rumors or trailers) of what they expect out of the MCU. Even many who saw the trailers didn't think they would lean SO FAR into the sitcom thing as WandaVision did the first three episodes.
My guess is they are trying to tell people with these little trailers, "please stay subscribed, it's gonna get crazy".