Final Fantasy XIV does not encourage players to have multiple characters. Even disregarding the game's somewhat strange pricing structure, you're expected to have one character because that one character can level every class and clear every quest. All that having another character does is slow your overall progress -- you'd only be doing things twice.
By contrast, Star Wars: The Old Republic all but insists that you make alts. The game's Legacy feature encourages you to level several different characters, and the fact that chunks of the game's story differ depending on your choices means that a single character doesn't see the whole game. Having another character enhances both characters to the point that filling your character slots is almost expected.
Most players fall somewhere away from either extreme on the sliding scale of alts. But let's assume you have a game that gives you only the two options -- have one character or have all the characters. Which would you prefer: a lone character who can do everything or an army of characters that collectively do everything?