Because when i was a consultant i had to bring my laptop to clients. A big keyboard didn't dit in my bag, but a TKL was still preferable to the laptop keyboard.
When I play games, I use a 60% and a Razer Tartarus v2. I won’t play any other way. It’s so much more ergonomic and better for my wrists, and I don’t have to rebind keys in games ever again.
For regular computing and work, I for sure use a full-size!