No plate change, no gasket, no case redesign — just a slot routed through the fiberglass near a switch hole. Flex cuts are the cheapest lever a designer has for adding give to a board that otherwise has none, and the cheapness is exactly why they show up where they do.
From 2018 through 2022 the typical custom shipped through one host vendor and a fan of regional proxies; by 2026 the baseline custom is a configurator on a vendor's own storefront. Boards moved. Keycap group buys mostly didn't.
Two years ago a custom-board recommendation defaulted to 65% with a polite note about 75% as the next step up. The KBD75 v3's staying power as a default recommendation, the QK75, and a crowded mid-tier have flipped that order. 75% is now the layout customs reach for first.