The main takeaway here is exactly this huge risk of gradual deterioration leading to invalid output that appears valid. That a thermometer fails in the hospital

The main takeaway here is exactly this huge risk of gradual deterioration leading to invalid output that appears valid. That a thermometer fails in the hospital or runs out of battery is not a major problem - another one is close by and procedures are in place to deal with it. Meanwhile, a wrong temperature read can lead to life critical decisions by the medical staff (ex. 39 vs 33). While I agree with your engineering tradeoffs perspective, failing safe is also a major recurring theme in engineering. When errors or loss of functionality happen they should be obvious and stop the system (machine + human operators) from spiraling out of control. A compiler won't silently write integers to a byte* pointer, because that might kill your patient where the parameter goes over 255. A failed display is preferable to a working display that outputs wrong data. By the way, 14 and 16 segment displays are widely available in passive LCD formats and draw the same power, while the upgrade to dot matrix LCD is not that prohibitive, I had it on my MP3 player 15 years ago.