As a millennial, like much of my generation who loves good coffee, I'd say it's primarily because we don't want the usual shitty instant coffee packets - Nespre

As a millennial, like much of my generation who loves good coffee, I'd say it's primarily because we don't want the usual shitty instant coffee packets - Nespresso & similar is a good way to get a decent coffee without too much faff/cleaning (ie my proper machine at home is more expensive, harder to clean & maintain in an airbnb context). For previous generations the same effect would've been before hotel rooms had TVs; there would have been a stark difference between hotel rooms that did and didn't have TVs for boomers (and maybe GenX?)