another major reason for ditching it is that all the series must be x-value-coalesced, so it's impossible to remove/merge datapoints along any single x without incorrectly removing/merging them in an unrelated y.
since the path is drawn directly from the data without any intermediate data->path conversions & allocations, i dont think there will be a reasonable point at which general path simplification would provide a net positive.
i'm pretty sure dygraphs does some form of simplification which seems to render well, but overall it ends up slower (not necessarily due to this, but did not check). it was also written at a time when Canvas was not as fast as it is today, so maybe it made more sense back then.