The most likely explanation is as the time duration reduces, flagging becomes more of a dominant factor. Unfortunately flagging is effected by factors that can have nothing to do with chess skill and are completely out-with the players control. For example, physiological reaction, local equipment lag, internet lag, and of course if you don't have a paid subscription Ads lag.
On top of this, it may well be that the weaker a player is the less their chess skill can compensation for such factors.
Aside from flagging there may be other non-chess skills that come into play, for example pre-moving. One would expect frequency of play would kick in as well, people are likely to play formats that give the highest rating. and v.v.
As for GMs stealing other people's rating... yeah that is how it works I think. Hikaru steals rating from Naroditsky, he steals from an IM, IM steals from CMs and NMs, who steal from strong unrated players, who in turn prey on the rest ...
When two active players play (let's say they both have the same RD) the game doesn't add or subtract any rating points from the pool, so a Hikaru and Naroditsky match doesn't do what tygxc is saying a new GM does. What tygxc is talking about is when the point-to-skill relationship is altered by points being permanently added or removed from the pool.
For example if by some error all your ratings were set to 1000, then those points would disappear, and the cost of returning you to your correct rating would be evenly shared by all other players.