Trying to force people to buy gralat packs by pinching income sources or devaluing the objects we've already paid for with the assumption that they would have some intrinsic value at a later date.
The actual problem, however, is lack of a clear monetization strategy in general.
This has been a problem for the game as long as I've been here... there's no clear motivation other than impulse purchasing and the (rather frowned upon ethically) drive to complete collections on a time limit.
Enough of using the stick, guys. Start using carrots.
Give players select benefits for purchasing packs.
Give them freebies. Prize Draws for players who have purchased a pack in the last 6 months. Give them special discounts on stuff. Give them a player experience where they feel that they're special for contributing instead of punishing them for not doing so, dangling objects with a massive price tag in front of their nose.
There's a ton of games that have systems completely devoid of any in-game bonus for making in-app purchases without making players feel like they've missed out because they haven't spent any money on an event. It's a delicate art.