Riot tried this, a super long time ago, and ended the program pretty fast because the recidivism rate was high enough that it was completely not worth doing.
Here's the thing: If a player was negative/abusive enough to get permanently suspended, that player had numerous warnings, chances, and scaled punishments before it happened. A permanent suspension is a demonstrated lack of reform by the very nature of how the systems work, so affording another chance after that point becomes pretty unnecessary.
With the particular example you're using, there is a lot Riot has to do just to keep this running, including:
- Designing the program in the first place
- Allocating internal resources to it
- Receiving smurf usernames
- Validating smurf usernames
- Checking in with the smurf usernames consistently
- Unbanning main accounts
- Ensuring those main accounts remain untoxic
This is a ton of work for a system that has already been tried in the past and had a failure rate of over 80%, so I can't really see Riot ever springing for it.