The same could be said for disc brakes, but we don't get annoyed about brands not adding a brake bridge so that we can still run rim brakes. The main advantage of the new derailleur is the way it mounts, it also allows them to get 13 cogs on the cassette but I would say that's more of a by-product. If you don't have a frame that allows you to take advantage of that mounting style, then buying the new derailleur would be pointless anyway.
The same could be said for disc brakes, but we don't get annoyed about brands not adding a brake bridge so that we can still run rim brakes. The main advantage of the new derailleur is the way it mounts, it also allows them to get 13 cogs on the cassette but I would say that's more of a by-product. If you don't have a frame that allows you to take advantage of that mounting style, then buying the new derailleur would be pointless anyway.