All of this is purely driven by cost cutting.
Many jobs require deep concentration and quiet and in places that respect this you get individual offices (extremely rare for the entire company, but notice that in 99% of companies every level above manager tends to get an individual office) or team offices (probably the best compromise in terms of cost - socialization trade-off).
The flexible desk ("flex desk") setups work for some things, but they tend to suck, too. You have to take everything with you, generally. Over the ear headset? Bring a bag! Favorite mug? Probably the same. Pens, notes, whatever? Nomad life style.
This probably the true for those big and famous offices (especially the part with interns). But "Architects" is broader group then that. Smaller offices often do consider internal spaces. Also sometimes it is often challenge to design it in way that can survive yak shaving [1] in commercial projects.
[1]: this one often occurs even after original budget was met in the design. That is why public projects are more attractive to many architects even if they are often more modest.
As a rule of thumb, main architects are just sellers. They sell projects to clients and authorities - only. Most senior architects are project managers, they don't plan anymore, at most they give some ideas and impose limitations. The rest, including "interns", do the bulk of the project, interiors or facades.
To be fair the working space is being experimented upon. The open spaces are fairly new, and there are plenty of workplaces also where people don't have attributed desks, they just walk around the building and sit wherever they want. Whether any of it works, I don't know...