Digital thermometers are certainly can be very very accurate but the cost of accuracy can be extreme. Few are willing or even able to spend the cash for a truly accurate digital one. The unit I use at work was over 600$
The issue is constancy during manufacturing. Cheap digital thermometers work based on electrical resistance at different temperatures very small amounts of resistance. A poor wire bad solder joint, bad contacts, bad board or anything else will throw off the readings.
Analogue are usually a bi-metal spring the ability to have two metal springs the same size constantly is not very difficult. The problem with some analogue ones is the cardboard face. They are often not assembled well. The advantage is that you can go to the store and check as many as they have and find a bunch that read the same, typically that makes them accurate as needed.
The fact they can really only measure the ambient air temp is a second disadvantage as this is one of three measurements that are needed. The others need a probe to get easily.
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