I'm afraid the answer to this question is not particularly insightful or interesting. It only has to do with how people working in different fields have historically defined the standard temperature for their work and which definitions are most convenient to work with.Unfortunately for students trying to keep track of different sets of conditions as they learn chemistry, people in different branches of thermodynamics have chosen to use different standards. In fact,another common standard that you'll probably come across is 293 K (20degrees C); it all comes down to who is defining it and for what purpose. In most real-life experiments, 298 K is a good standard because it is approximately room temperature, but keep in mind that temperatures vary between labs.