This is not a surprising conclusion given the way things have gone. The collapse of the natural origin theory (which was based on various schemes involving co-infection of bats, pangolins, civets with various wild-type viruses which didn't pan out) and the refusal of the Wuhan Institute of Virology to have an open investigation, along with the fairly shady behavior of the Ecohealth Alliance partnership that was partially funding the WIV (not disclosing conflicts of interests in those early Nature and Lancet letters claiming a natural origin), all result in a 'so what else could it be but a lab leak' circumstantial conclusion, even if positive evidence remains hidden.

What kind of lab leak is an interesting and important question, however. There may be four scenarios:

1) Collection of a wild-type virus that somehow evolved in a bat species, followed by accidental infection of a lab worker. This seems the least likely, as the viral lineages of the betacoronaviruses that would have had to fuse in the wild to form Sars-CoV-2 (sarbecovirus w/o furin site and marbecovirus w/ furin site) infect different bat species from different regions;

2) Collection of a multitude of wild-type viruses as well as a variety of bat species, then having accidental genetic fusions due to coinfection of the laboratory bats with a variety of different viruses (like what seems to happen on pig farms with avian / human / swine flu), which might be more plausible, though would indicate incredibly sloppy lab management;

3) 'Natural' mutational pressure via deliberately cultivating wild-type bat viruses in human cell cultures or in mice etc. expressing human genes, and looking for rare mutations that arose and gained the ability to infect human cells (things like this were done in the Soviet bioweapons program according to defector Kanatjan Alibekov, see "Biohazard") or to become more infectious than it already was;

4) Direct gene manipulation of wild-type (or possibly mutated) viruses using CRISPR technology, in which parts of the wild-type template virus are excised and replaced with specifically synthesized new sequences designed to bind to human receptor sites to facilitate entry to human cells by the virus. It'd be likely they synthesized a variety of such chimeric viruses and then ran them through human cell cultures to see which were the most infectious. They were doing this kind of work at Wuhan, based on prior CRISPR-based work done in the USA c.2015, and it seems most likely that a lab worker got infected then passed it to the local community, then onto the trains and airplanes.

Notably, 2-4 all could be called 'gain of function' research, which is a sloppy term that nobody in the field seems to use. It's all pretty reckless and poorly justified research, and people have been warning for about a decade since these precise gene swapping technologies became widely available that this kind of outcome was likely if not inevitable. It's also basically indistinguishable from offensive biowarfare research, even if that wasn't the goal (claims that this was deliberate are nonsensical, it looks like a "oopsie, we caused > $10 trillion in economic damage and killed millions of people by accident" event).

International collaborations to fight infectious disease should still be supported however, that's how smallpox was eradicated. Just not this kind of thing, please.