They can and they do [1]. They just don't have the same marketing budget, so you don't hear as much about them.
All BS, and when I asked if they'd fill a prescription for lenses for my VR unit instead of ordering them online, they stared at me like I had grown a third arm.
I hate hate hate EssilorLuxxotica.
BTW, the app is called PD Measure.
It's called a PD Ruler and it's literally just a mm ruler. Bald-faced liar indeed.
The glasses I got from my optometrist are much better, at 3X - 4X the price of Zenni.