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There's no technical reason why the unblocking can't be done via software. Only possibilities are that:
1. AA doesn't want to implement this software feature
2. AA doesn't want to bare the cost burden of implementing this software feature.
No, the reason isn't technical. If you read the article, it states that American's customers don't WANT seat blocking. Nor do we want MRTC, free meals on board, or food in the AC. If you would just AA, then you would find out what it is you really want.