It was a fringe theory pushed largely but not exclusively by racists and opportunists that wanted to paint China as the bad guy and shield the previous administration and other politicians from blame for how they reacted to the pandemic.
Totally independent of that, the general scientific community seemed to be much more opposed to the lab theory early on than they are now. It still doesn't appear to be much evidence for it beyond circumstantial stuff, but it is a possibility that more people are engaging with.
Combine these two and it isn't surprising that these platforms cracked down on this type of talk early and are slow to allowing it to start happening again.
Totally independent of that, the general scientific community seemed to be much more opposed to the lab theory early on than they are now. It still doesn't appear to be much evidence for it beyond circumstantial stuff, but it is a possibility that more people are engaging with.
Combine these two and it isn't surprising that these platforms cracked down on this type of talk early and are slow to allowing it to start happening again.