Office is an external discipline forced on you while WFH is an internal discipline no one watching over your shoulders, that's the difference.
For an undisciplined person anything can be distracting: birds chirping, picking up a delivery, cooking, a friend dropping by, daily chores like washing, organizing things, etc... it's an endless list really.
It is not easy to say that I'm not a very "internally disciplined" person. I once spent half a year procrastinating instead of working on a personal project. But when you're working for someone (regardless of place), they are paying you for it, and you would like to continue receiving the money, how is this not externally enforced discipline?
I've been WFH since 2016 and I never had an issue with focus when doing paid work. I do want to get paid.
Undisciplined people distract themselves in the office and they happen to distract all other workers around them too.
If you can't tell whether your staff are working that seems quite orthogonal to WFH.
> no one watching over your shoulders
That alone is distracting enough for me. I hate the "look busy" vs. actually being busy game people play in offices.
I have severe ADHD and I don't even know what discipline feels like. That's precisely why I can't work in offices. In fact, other people are more productive when I am not in an office with them as well.
I'm cursed with the fact that a lot of my hyperactivity manifests as talking. It's actually problematic enough that I have been reprimanded for talking excessively at points in my past. I am quite charismatic too, so people end up getting locked in these hour+ long conversations with me lol.
At home, there is no one talk to but my significant other who often works during the same time. So, WFH skyrocketed my productivity. I go in the office two days a week, and I basically lose two days of work a week now.