Up through about 12U, teams have changed their yearly rosters by:
Dropping a few kids and picking up some better talent.
Dropping half your roster and joining with another team's half roster.
About age 13U, you will start seeing Coaches that stay at a particular age group and therefore do not have players from the previous year to take. Top talent from the age groups start to gravitate toward these teams/coaches. This can leave some teams that were hoping for a strong continuation of the previous year, with no horses to draw the carriage.
How many coaches from the current 13U teams do you see staying down to coach 13U again? I only know of 1 and that is with an east cobb team but you see this more at 14U and older more so then 13U. And I don't think it's even that wide spread since even paid coaches will many times move up if they stay with the team they've coached with in the past. So, in the end the shuffle won't be that much different then previous seasons except this year there seems to be more teams breaking up for different reasons.
Interestingly, I wrote this post based on waking up this morning thinking about several 12U teams, as you also mentioned, are breaking up or have coaches that are going in different directions. When I compared that to when my older son went through this age, it dawned on me that the team changing occurs for different reasons starting about the 13U age group. This go around may be different.