It doesn't need to be so. I started in my actual company 3 years ago, NY based startup and I was based in Europe. The first months we had every day meetings with one of the senior engineers in USA going through the changes we implemented that day, how it worked with the rest of the codebase and systems, how and why this worked and that didn't, etc... It worked perfectly, considering we still work in the company and we are know the seniors. The system we started working on, that was freshly released then, is now smooth and stable. We did it full remote and also with a 6 h difference in time zone, and it worked.
The thing is the time investment may look big because you have to specify a meeting time and reserve a slot of an hour for it. But it is not different from having it spread across the day as the juniors find a problem, interrupt the senior, get the explanation, etc.
I worked in both environments: in the office and full remote. And regarding work and knowledge sharing I don't see a big difference. The real difference is changing the way of working and interacting, but once that is done it works equally fine. The rest is a matter of preference related to interacting with people on a daily basis. But for me, that is outside working hours when I go to the gym, join activities like quizzes, sports, etc., with people I don't work with.
Also I want to add that I connect in videocalls with colleagues, when we have not much work for a few hours just to chat about work and out of work things. And we never met in person.