My guess is that it has less to do with leaks and more to do with how experienced the teams are. EA has had a lot of staff turnover in the past few years and it's difficult for a newer dev to work on an older IP, so a team with a bunch of new devs are probably going to create a product that is less compatible with existing software than one who is very familiar with it.
I think this also reflects the level of gameplay each pack has. High School Years and Snowy Escape have fewer features than Cottage Living and Eco Lifestyle. Werewolves has more gameplay than My Wedding Stories and fewer bugs. I've never bothered to compare the names of the developers and see which ones repeatedly create a low bug/high gameplay software but I think that's what it is.
