Repeating plastics tends to damage them on a chemical level. The polymer chains break and shorten. This ends with the plastic being more brittle. Since 3d printed parts have already been remelted once, they have even more degradation than injection moulded parts.
I believe the recommended amount of recycled plastic is around 30% for PLA. Any more and the parts lose significant strength.
I personally would prefer us to accept that plastics aren’t really recyclable. It’s better to move towards renewable plastics like PLA, and treat the waste as biomass (either composted or burnt for energy.