I was trying to print something when my new Samsung Xpress M2020's app hit me with a very irritating pop-up asking me whether I wanted to share data with its software (this also got me paranoid, but that's a question for another time). I clicked on one of the links provided in the pop-up to get more detailed info regarding data collection policies and the link opened up in Internet Explorer. I'm running Windows 10, and I double checked that my default browser is set to Edge, and when I don't use it, I use Chrome. That freaked me out along with the fact that I have IE in the first place. It is also not listed amongst other apps/programmes in the control panel, which freaks me out.
Executable programs on a PC have the (potential) ability to call any other program they wish (assuming they are programmed to do so). Programs do not have to honor "default" file association settings nor do they typically look at what you most frequently use.
Regarding IE, Windows 10 still has it installed by default, even though Edge is now the official Windows 10 browser. You can type "Internet Explorer" in the Windows 10 search and you should see it appear in the results.
As pointed out by @AHF in the comments, IE is assumed to be on every Windows system and thus makes a good choice for displaying .html files.