Somehow nobody's managed to give a reason that i've seen.
The reason this isn't a feature is because it would result in people disregarding the quality of their mods and just spamming one-change mods for Kudosu. This would probably not fend well for the current beatmapping community as there will be more mods dolled out, but of less quality than they were prior to the change.
TL;DRThis isn't a feature because people would disregard quality for quantity to "rank up" in these new Kudosu rankings.