Seriously? I was making 50mil a month when crab bows and jade crooks were cool.
Admittedly it has become a lot harder to make money since then and I've barely had a retainer in a ward this year because I just can't be bothered with it any more, so I can see why a new player would hold the opinion you have.
These days gil is mainly made through selling lots of small value items rather than high value items like +3 weapons. Sure the relic double melded weapons are expensive, but chances are if you're making those you're buying the materia so the profit is very low. It's just too time consuming to farm the right materia due to the RNG.
But just the other week I made over 22mil just exchanging my guildmarks. Money for literally nothing. I bet most people exchanged theirs without even thinking how to get the most money per mark.