The software version of widevine would be so thoroughly broken in a very short time that it would be bypassed by any one-click downloader addon. Nothing would change for users and YouTube would have the overhead for widevine.
Using the hardware based version could cause a lot of problems with unsupported devices.
As another commentor pointed out, Widevine is already in use on many streaming sites. Where are the one-click downloader addons for those? If they exist, I have not been able to find them.
(My use case is not so much in downloading a video, I just want to be able to my Amazon Prime videos on my Linux computer at a better resolution than 720p.)
I used results from this Github search page (especially pywidevine) a while back to make a Hulu downloader in Go which I eventually had to remove:
https://github.com/chris124567/hulu
I wasn't really a part of this scene but there appears to be some sort of weird competition among people involved in writing this kind of software so occasionally device keys would leak when they tried to get at each other which was great for me because it meant I didn't have to extract keys from a phone or NVIDIA shield or anything annoying like that.
You are probably already using the software version of Widevine (L3) to watch 720p content in the first place.
There are relatively easy ways to download L3 content, but they are not as common because higher resolutions are available on illegal streaming sites and torrents. These sites break hardware Widevine or use other attacks to get the material.
While that sounds reasonable, is there any evidence that this is the actual reason? Widevine is also used by other ubiquitous services such as Netflix, Prime, Hulu, etc.. and yet WV still remains an insurmountable barrier for most people, even in its weakest form (L3).
Good points. The difference is that on streaming sites, L3 widevine will only allow low resolution playback. They are also tied to a paid account, making it much more difficult/risky to download content. Even if the encryption is broken, there are often ways to detect such users for a limited time.
For professional content, there is simply not much demand to develop a user-friendly way to break L3 widevine, as the market is already served by reasonably convenient illegal streaming sites and torrents that allow for higher quality video.
Using the hardware based version could cause a lot of problems with unsupported devices.