That is a fair point. If they are not busy there is not really any reason to not offer a tour. But I can also understand why they heavily prefer appointments. Having random people show up and interrupt your work can be annoying.

It's a communal space. If they see me coming in to an open area as "disrupting" that's probably not a community I'm interested in anyway.

It's not like I was requesting to see a meeting room that was in use.

Appointments are not unusual when arranging for commercial space. Norms are similar to any other professional/B2B environment. I suspect it's a filter. An appointment only process allows the property managers to notify current tenants beforehand; to schedule around shared facility use (e.g. conference rooms); and to research what's available when for how long.