To be completely honest, its just how the system works. Percentage of d4+ players is so small that lp changes are dependent on keeping players in the average %s of their ranks. In other words, in order to maintain that .xx percent of players, the lp gain/loss fluctuates simply because skill level necessary to climb higher is so great because of the so little players.
If you really think about it, they're are only a couple thousand people who have a higher rank than you. To make sure there is actually a difference between each rank to master and challenger, lp gain/loss is very different and you're going to need a multiple game win streak to even think about climbing. That's how it works and it sucks but at least it keeps the boosted players out, just gotta play very consistently I think to climb.