They're not scrapped, they just don't actually follow any sort of set schedule. :)

I'm pretty sure at this point that guaranteeds aren't making Plarium any money anymore. Patient players (not me) are now sitting on stockpiles of shards. And Plarium can see the exact size of these stockpiles. it's a rigged game, "we" the community will never "trick" them into giving up value. It's a monopolist pricing problem with full information.

Their increase in the number of shards required has been very unpopular, even though these offers went from amazingly awesome deals to "just" good deals. 

More importantly, it is a constant reminder to players how bad the drop rates from shards actually are, and how much undesirable crap there is in the leggo pool. Fusions are a bit similar, and Plarium has also been tightening the screws there. But they also drive a ton of engagement with the game. A month's worth of hype and discussions for a good fusion, as opposed to a few days for a good guaranteed.

I don't think they can increase the requirements for guaranteeds even more, unless they start giving advance notice. I could see a series of events where you earn fragments for a champ, purely from summon events, over 4-6 weeks. But guaranteeds at more than 20 leggos are just not happening. The sticker shock is too much. I also don't think Plarium will be happy with fewer than 20 shards. So where does that leave them?