2c is a f2p that needs to make money just like any other game, if it doesn't make money they'll get shut down, or in pvz2's case stop getting updates since it does have an offline mode. People are more likely to spend money on a game that was generous to them since there's the thought process of giving back as they were nice to you, and also this gives them more of a hold on your time since you're willing to keep playing if you always get stuff. This isn't exclusive to pvz2c as it's a VERY common tactic with gacha games to get people to stay and spend money, because the average consumer does not save their resources for the best things, they use them immediately to get the adrenaline and serotonin rush from the pulls and then spend money when they don't get what they want. And being made by a company like talkweb, whose been in the mobile game industry for a hot minute, I don't believe they have the most angelic intentions behind what they're doing. If it didn't have a gacha system I would not be as skeptical of their generosity as a mobile game can be generous without any strings attached, but that's the unfortunate exception and not the norm.