They take up a lot of real estate on a display and aren't particularly easy to read unless you get up close. If you already know what thresholds are it is far better to display a number and use the color to indicate where that is within the continuum of states.

There are practical uses for steam gauges, but I would argue that monitoring complex IT systems is not one of them.

Taking up lots of real estate on a display is kind of the point of high-visibility indicators.

Regarding "aren't particularly easy to read", are you talking about reading numbers on the ticks? That's not the point of those indicators; the point is to be familiar with the low/expected/high ranges of the needle for various situations and be able to see with clarity the current state of expected/unexpected range of an indicator. Which then can be further inspected if necessary to focus in and see an exact number.

> If you already know what thresholds are it is far better to display a number and use the color to indicate where that is within the continuum of states.

Since this thread is already on the topic of accessibility, I feel compelled to point out that this is the single worst option when considering colorblindness unless you mean shades of one color.

Many automobiles actually have started using numbers instead of a radial gauge. It has even been suggested it actually prompts drivers to speed less when they can see they are doing 74 in digital rather than convincing themselves the needle is resting on 70.