Why are modern thermometers so shitty. Maybe they work well if you spend more than $100 on them. In the $30 range of oral or ear thermometers temperature readings can vary by as much as +/- 2 degrees. We have three thermometers and all three are just fucking garbage. All three have decent reviews on Amazon, all three have been calibrated and all three can only tell you if you have the warmth of life but not much more of any practical use. I'd spend $40 on an old fashioned mercury thermometer.
Simply put? The FDA. The thermometers you're talking about are thermocouples. Thermocouples aren't crazy hard - you can get really precise ones for not a shit-ton of money. But then you have to get them FDA qualified and if it's something that can go in an orifice - any orifice - it's in FDA hell-world. So you take a $1 thermocouple, a 50 cent display board and a 20 cent plastic body and it's suddenly a $30 digital thermometer because $26 of that is the paperwork and testing necessary to get it FDA-approved as a healthcare product. If you go with a not-stick-it-in-a-hole thermometer you capture more of the raw technology and less of the regulatory oversight. Sterilization and contamination protocols for a contact medical device are substantially more chill than for anything you put in your body. I've got a Thermoworks Thermapen. It'll read to a tenth of a degree in half a second with a NIST certification but it's not healthcare approved. We use that exergen jobby for the kid; you gotta swipe your forehead like six times and take the highest number.