They don't have that many people working on reworks, maybe 4 or 5 now (designers - there are lots of other people involved in art and other assets). There are also a lot of planned rework projects, but they take a long time. Gangplank, for instance, has been in the process of rework for over 6 months (and is on hold for the moment, I believe). We talk a lot about Riot priorities on the forums, but we can't actually see their calendars, plans, or failed projects. A lot of the stuff we ultimately see takes a LONG TIME in creation, testing, and implementation.
I do think Riot should be more upfront about their goals and plans to achieve them, but I can understand that things take so long.