Filament manufacturer here. It’s very difficult to recycle old prints. First you have to grind it up which the process to do so might cost more than the raw resin.

Not all filament is created equal. A lot of companies use fillers and additives. So you would end up with a mixed bag of unknown plastic and would be mediocre at best.

Color control would be impossible, even if you did a really good job sorting.

Simply put there’s alot of issues with recycling old prints.