I wouldn’t focus on niche places that do this though as an arguing point. It may as well be, “but some chipotle’s don’t offer guacamole. So, ya know, can’t rely on it.” Might be true but sounds rare.
It was acceptable to bring your own keyboard and mouse to two out of the five companies, other than that, no other hardware was allowed to be brought in. So you are stuck with the monitors provided, with the rest of the hardware that was provided, and while you could bring in limited ergonomic stuff, you were also limited to whatever office furniture was available.
People got away with breaking some of the rules, but it was definitely a risk - it was theoretically grounds for dismissal to bring in your own hardware, IIRC, let alone to run unapproved software.
The concern in that case was a PHI (personal health information) breach, which could bring the wrath of the US judicial system down on the company.
So, not top-secret or anything like that, but still very conservative and with decent reasons to be so.
It would be easy to figure that out about me, if you cared. Say if you found a list of employees and contractors.
A sufficiently-motivated attacker could backdoor my firmware with a timer-based exploit (e.g., start your keystroke payload after ten minutes without input events) and I might well not notice if it was a deft-enough change.
It might not be worth the cost, given that I might well notice it and it might not pay off even if I didn't.
Still - the point is that keyboards are not innocuous, harmless devices that it's a no-brainer to allow.
So unless the item is listed on that list, you are SOL.