I don't think they were slow, they did some fairly major reallocations a few years ago that were met with many more complaints than accolades, because people that were used to travel in a particular season could no longer do so without purchasing more points and now the charts resemble more of the originals.
It's basically is that you can't please everyone and people are used to the charts in the basic structure they were presented with...and they bought points accordingly.
Now it is true that many owners travel patters change over the years, but it is easier to plan for those changes with fairly stable charts, than having points change dramatically year to year. If points were in continual change, DVC sales would suffer dramatically.
And that is a big problem. While they can contractually reallocate points for demand, major changes, such as increasing points for early December, are likely to create no problems than they solve. There will be a lot of complaining, and ate possibly some lawsuits if the changes are drastic enough. Meanwhile, you drop the points to go in April, that doesn't mean April people a happy. Not every DVC member had unlimited vacation time to use all their points and you don't want to pay dues on points you aren't using.
And then Disney marketing adds rum to dole whips in April, puts in a bicycle race and a hot air balloon festival, or hosts an international Lego tournament, and then the points are out of whack again because you've increased demand.