There is a very plausible route to a lab leak event, and there's quite a lot of circumstantial evidence that supports it. Direct physical evidence is lacking because the Chinese government refused to allow an immediate investigation, and the one later allowed, the WHO visit, was not independent or empowered to investigate in a convincing manner.

So:

1. WIV researchers were collecting a wide variety of bat coronaviruses from natural environments for study and analysis under laboratory conditions. This work was done at least in part in collaboration with Ecohealth Alliance, a private institute funded by the NIH which has a record of doing wildlife viral research.

2. WIV researchers were developing advanced genetic engineering capabilities since at least 2013, work done in collaboration with the Baric Lab (Baric had developed the 'no-see-um' techniques for introducing genetic modifications into coronaviruses without leaving any typical genetic engineering signatures, such as palindromic sequences used in older restriction enzyme-based engineering methods).

So WIV had a large collection of bat coronavirues (whose sequences were stored in a database that was removed from the public web and has never been made available to investigators, raising suspicions that it contained a wild-type precursor to Sars-CoV2). WIV also had access to technology needed to make edits to the virus that were indistinguishable from naturally arising mutations.

Furthermore, they also had access to mice genetically modified to express the human ACE2 receptor, the target receptor of Sars-COV2. We know they had access to methods to modify the furin cleavage site of the coronavirus to make it a good target for the human furan enzyme, which allows the virus to be cut appropriately upon binding to ACE2 such that it is translocated into the (human) cell, where viral replication begins.

So: researchers could have taken a wild-type bat coronavirus and applied two experimental methods: first, get the virus to replicate in the mice (which bat coronaviruses seem able to do without any modification). These engineered mice probably express a mixture of human and mice ACE2 receptors. Then, introduce the human-type furin cleavage site into the virus, while continuing to do serial passage through the mice (collecting new virus from infected mice, passing into new mice, etc.) leading to 'natural' evolutionary changes throughout the entire virus sequence. These two methods could have been applied in the reverse order, it's hard to say.

Eventually, they'd have been able to culture the virus in human cell culture, and at that point they had a human-adapted pathogen. This would explain its immediate pathogenicity, in contrast to previous zoonotic episodes where intermediates are found in animal and human hosts - it was pre-adapted in the lab prior to the outbreak.

All it would take is for a researcher to get infected from the culture plates, then spread the virus to the local seafood market or to people on the train, and from there, onto airplanes and around the world.

This is an entirely plausible scenario that also explains why the pandemic originated in Wuhan. If only people could disassociate this technical explanation from the politics - and from the highly implausible notion that this was a deliberate release.

As far as why it matters, there are hundreds of wild-type mammalian (or bird) viruses out in nature that could be modified into novel human pandemics using the techniques outlined above, and continuing with this kind of research is highly unwise.