The Plants vs Zombies franchise as a whole started to experience downfall after the release of Battle for Neighborville, at least from my knowledge. The main reason that Battle for Neighborville was not very successful is due to unnecessary changes that were not needed. Garden Warfare 2 continues to be a great game though, and Battle for Neighborville still has its perks, so EA should have another go at creating a sequel in my opinion.
I agree that the Plants vs Zombies shooter games are very unique and that they stand out from other shooter games, and that is a large part of what makes these games fun. The content and gameplay really stands out, having special modes such as Ops and Infinity Time. The town hall events are generally great fun as well, although I really want to see Boss Hunts and the special events return.
I heard about Project Hot Tub or whatnot as well, although that and Plants vs Zombies Adventures were cancelled. A silly reason why Hot Tub was cancelled, I saw that on YouTube. Wow, the Plants vs Zombies franchise really has been suffering lately.
I really want to see the Plants vs Zombies franchise head in a positive direction, with no more cancellations, so that the community can continue to enjoy this franchise for a long time to come.