Sometimes it's easier to type "c" than "°"

First of all, the °C is not the metric SI unit for temperature. K (Kelvin) is.

Second, even with Kelvin, nearly all temperatures that matter for normal human issues happen to be below 4000K, usually way below that mark. And with most of those temperatures, about all digits usually count. A core body temperature of 310K or 313K makes a BIG difference for the person involved.

In settings operating with more than 1000°C they would opt for Kelvin instead.

It's probably more common that scientific notation is used. So 3.2 *10^4 or simply 3.2e4. From the little physics I had, you often used kilometers instead of something like megameters. Or used just lightyears when you got on a big enough scale.

[Edited because of weird auto-formatting. Edit 2 added more pedantry. Edit 3+ is because I lost the plot and had to bring it back.]

Because the SI unit for temperature is the Kelvin, which has already been stated. It has also been mentioned that K and °C are the same but with different offsets. It has not been mentioned that °C is to K as Degrees Fahrenheit (°F) is to Rankine ( R). It would be similarly inappropriate to say "millidegrees Fahrenheit" or "kilofahrenheit". I have no idea if mR or kR would be appropriate, though.

I would offer that there are two ways to look at SI ("metric") prefixes, and these can be thought of similarly with the multipliers they represent: as a prefix to the unit, by definition; or as a suffix to the value. Let me illustrate with an example.

38,000 K could be expressed 38 kK, or "thirty-eight kiloKelvin". It could also be spoken "thirty-eight thousand Kelvin" (or Kelvins, idfk). This isn't normally important for the layperson, but suppose you have a temperature meter (and, literally, I do not mean "thermometer") that has only 4 digits of resolution. 38.00 k ("38,00 k" for the Europeans?) would be how it reads out the value in question. This would be 38 kK, certainly, due to the position of the decimal.

Now suppose that temperature meter read out in °C. 38.00 k °C would, in fact, denote "thirty-eight thousand degrees Celsius" for the reasons mentioned above.

So, because Degrees Celsius is not an SI unit, in the technical sense...

Btw, I have been explicitly using upper case letters when spelling out the units. This is incorrect. The symbols for SI (International System of Units) units should be capitalized when they respect a person (K, A). The names of the units should be all lower case because you are not naming the person, but the unit named after them (kelvin after Lord Kelvin, and ampere after Andre-Marie Ampere).

Yeah, I know. I'm being pedantic. It's literally my job. I really should be sleeping right now. Here's a source: https://www.bipm.org/en/measurement-units/si-base-units

Interestingly, I hear people use terms like millikelvin and microkelvin often enough, but never kilokelvin. In fact, there are some hilariously impractical ways to avoid large scientific notation for Kelvin. There's T4, which is the temperature in kelvin divided by 10^4, and there's electron volts, which is almost the same value, but preferred by different fields.