The custom mechanical keyboard community has been slowly growing for years and at the high end figures probably weren't too impacted by WFH since the supply is as constrained as ever. The "good" stuff is run as group buys and typically sell out within minutes. Satisfaction75 had 1300 units available and sold out in just over 10 minutes, smaller runs like Iron 180 or Bauer 2 sold out in something like two minutes. Those examples are all from the fall.

And this is not a hobby for the impatient. Group buys take your money now, but often don't deliver for 6 - 12 months.

Some keyboards are unlimited (e.g., Grid 650), but that's typically not the norm.