Why?
miles are miles, has someone shortened them?
Outdoor miles are not the sacred and shall not be contaminated with indoor miles.
I would never suggest those who commute or cycle leisurely are not adding up mileage compared those who train hard to build fitness on the road. Same goes for indoor mileage or outdoor. Its just a measurement by which Strava indicates how much time you've spent on a bike. If Strava and alike swapped their primary measuring stick for TSS, would you then argue outdoor TSS is only to be counted?
I count them as part of my total. Most people who ask me how is my cycling are non cyclists and understand instantly mileage, I then go onto describe my training involves mostly indoor work, by which point most have glazed over

My cycling buddies are overall impressed by the hours of time I ride indoors to their outdoor. When we meet up for sportives, tours, we are all pretty much fit as each other. Its just we all do it slightly differently.
Wow, I managed to complete a post and not say 'Door handle'