A door isn't that helpful when everyone can just ping you on Slack anyway. And it's not like you can close the app for a while, because then people think you're unresponsive and unhelpful. Especially when 1/3 of your team is remote.
But I can mentally snooze a Slack notification for three minutes or so, enough to neatly tuck away everything in my head and reach a state where I can more easily resume what I was doing. That doesn't work as well when I have someone breathing down my neck who "just wants a really quick word".