Because every conference is its own bubble of enthusiasts and SW engineering is a lot more diverse than Ruby, from C++ kernel devs to Firmware C and ASM devs.

Even the famous FailOverflow said in one of his videos he only bought a Mac since he saw that at conferences everyone had Macs so he thought that must mean they're the best machines.

Anecdotally, I've interviewed at over 12 companies in my life and only one of those issues Mac to its employees the rest were windows/Linux.