Stomach acid doesnt break down many (possibly most) of the toxins that bacteria and mould produce, which can already be at high concentrations in contaminated food. So whether or not the bug survives or not doesnt help you.

Bacteria that cause gastrointestinal infections have various ways to survive digestion. Salmonella for example relies on being consumed at the same time as food and being digested in high numbers, when you eat a meal, the food offsets the pH of your stomach, making it closer to neutral. Other bacteria have specific protective mechanisms against stomach acid.

Also stomach acid isnt all that acidic, you would know when you throw up your tongue doesnt dissolve away or anything, its not equivalent o the acid used in acid attacks for example.