That's literally what a gain-of-function experiment is. These are done to study how viruses interact with humans so that we can deal with them better. There's nothing sinister about it, such experiments are happening all over the world and they did happen in Wuhan.
Did you just reply to the sentence I quoted or did you click the links? The tweets are very obviously not limited to that: https://twitter.com/ehundman/status/1246598376377831425
And honestly, it's hard to go from "this happened via natural selection" to "nobody dismissed this coming from a lab". Even if it's technically possible, surely you can understand why readers' message from this is not "this could have come from a lab".