Window “Cabinets” Containing Insulation?

[swissarmyscissors]

Hi! New to the board. Thinking of buying a PNW 1950’s home with an odd feature I’ve never seen before. Hoping someone here knows about it because it’s intriguing! on either side of almost every window in this house, there are cabinet-like doors. When opened, they reveal a huge piece of insulation, cut so that it can be easily removed from the cabinet and then replaced. Behind the insulation is the backside of the exterior wall. Straight wall. Wooden slats are visible. So strange! Our best guess is it’s some kind of old-school cooling mechanism where you remove the insulation to let more air circulate or something. But that doesn’t sound right. Any ideas? Will try to get a photo this weekend when we go back. No idea why they left this feature either when they redid the rest of the interior.