The argument of paying for a game once upfront and playing it whenever you want vs paying a subscription fee never made sense to me. I can make a very long list of games I payed $30-$60 for, beat once, then never played again. There's nothing new to experience in those games. Once you're done the only option is to do it all over again. For subscription MMOs it's not so easy to complete everything. You pay a little each month but each time you play you're seeing new content or getting further in content you've done before. You could spend a month in FFXIV leveling up all your skill jobs. Or getting better gear. Or exploring new dungeons. Then do something completely different the next month. You pay to continue to do new things.

OOC:
I've had the same experience with WoW since I started after Burning Crusade and wished I'd see what endgame was like in Vanilla and how those zones worked. Or a time when Taurens didn't get mounts because they had Plainsrunning.
I could answer those questions and experiences Plainsrunning for Taurens was in Beta only though. I wasn't in Beta.