Do airports or airlines disclose the number of checked-in baggage thefts reported by passengers every year, and is there a central database where one can find and compare those numbers?
A 2012 Conde Naste Traveler article notes that
Statistics on baggage theft are hard to come by; the airlines don’t compile them, and if a journey involves multiple legs, it can be difficult to prove where the theft occurred. The TSA, which collects information on lost property, reports that between 7,000 and 14,000 claims are filed with the agency each year. Just how many of those missing items were stolen by screeners, versus baggage handlers, will never be known. …
Airlines hand off bags soon after they are checked to screening personnel (who may work for a security contractor rather than the government), and then to ground handling companies (again, often a third party rather than airline or airport employees), plus customs inspectors on international trips. Considering this, each airline's Contract of Carriage includes a clause limiting their liability for missing or tampered bags, and insulated from litigation, they have even less incentive to involve themselves in how bags find their way on the ground.
There are a few proxies for this data. In 2012 ABC News requested personnel records from the TSA under the Freedom of Information Act and reported on employees dismissed for theft. You can also track the number of complaints filed by passengers regarding theft. But these are imperfect, and only cover the U.S.
Another imperfect source is a 2008 study by the Ponemon Institute, a security consultancy (and thus a company that might benefit from public concern over theft, sponsored by Dell Computer's security services division, which absolutely would benefit). The study is flawed (seriously, multi-dimensionally flawed), but I mention it in the hope that it inspires you or another poster to remember a better study or source. LAX and LHR fare worst, but of course these are also two of the busiest airports in the world. In contrast, most anecdotal complaints of theft I have heard from travelers involve airports like NBO, LOS, and JNB.
The best assurance against theft is to have nothing of value in your checked bags, especially electronics, jewelry, drugs, or other small items that can easily be slipped out and concealed along the baggage handling chain. No one will be rifling through your bag to snatch toothpaste and socks. If you must, carry plenty of insurance as well.
Do airports or airlines disclose the number of checked-in baggage thefts reported by passengers every year
Some do, e.g. there were 96 reports of stolen bags made to the San Diego airport (SAN) in 2022. That doesn't take into account reports of stolen bags only made to the airlines.
Source: https://youtu.be/WDOR0oT9PA4 (the screenshot is incorrect, it's not "96 stolen bags" but 96 reports of stolen bags):