72 pixels per inch is not a part of the image, it's an embedded number which is used in the program which you use to watch or edit the image as a guidance how big the image actually is as inches. The number tells nothing of the quality of the image, it's only number.
Program and devices which are used to generate or edit images insert often just that 72 ppi as a default value if nobody programs something other value to be used instead. Image watching and editing programs calculate the image dimensions as inches or millimeters from it and the pixel dimensions.
72 ppi is the common default value, beacause a long time it was close the usual pixel density (=resolution) of common (see NOTE1) computer screens, but in photo editing programs GIMP, Photoshop, etc. one can easily change that number to some other. I change it often to 300 ppi because that is common resolution for printed images and I can see the printed size easily in layout programs. Any other number is as acceptable, only the pixel dimensions mean something for how sharp an image actually can be and how much information it can contain.
WARNING: If you decide to change the ppi-number you can easily spoil your image if you accidentally also allow the program to resample the image to other pixel dimensions. So, do NOT allow resampling if you decide to change the ppi-number, but want to keep the original pixel dimensions and the true image quality intact.
NOTE1: Actually it was state of the art 35 years ago and it was still common 10 years ago. Today in 2022 many people have much denser screens.
ADD: There's another answer and comments which seem to be based on knowledge of history and have some idea how 72 ppi happened to become selected, not for ex. 82 ppi.