[kragen]

diodes are cheaper, smaller, and easier to solder than transistors; ttl took off with integrated circuits

ttl was the default choice for building discrete logic circuits until about 01980, after which point it was obsolete because cmos (74hcxxx, not cd4xxx) was better in every way except esd

if you're running an educational computer lab on a tight budget, esd is still the dominant consideration, because students will burn out all your cmos chips with static after only a few dozen uses, while ttl chips will survive most of their mistakes

but outside a circuit lab or possibly repair of 40-year-old devices there's no reason to use ttl