Yeah, because it’s fast and little pain can be felt before its dead. Guillotines were developed to be a more humane execution for people.

“Physical methods” (Guillotine, cardiac puncture, thoracotomy, etc) are usually a secondary confirmation of death after lethal ketamine/xylazine cocktail injection, isofluorane, or CO2 inhalation.

And yeah we’re sacrificing them to the science god to try and make new discoveries and new therapies. We’re also trying to develop ways to avoid using organisms such as organ on a chip or multiple organ on a chip systems but thats expensive af and not yet sufficient quality to replace organism testing.