I don't understand why ranked doesn't have any meaningful/interesting rewards other than a portrait frame and some crystals that even people who don't play ranked have more than they know what to do with.

In another game I played, you earned glam with each higher tier of rank you hit, with a full set being awarded at one of the later brackets. I could see FFXIV ranked players enjoying a similar such system, but with full sets of glam (perhaps getting more elaborate with the higher tier stuff as you go) rewarded instead at each tier. Every tier would also reward everything from the tiers below it.

I've read and heard that the top ranked players in the past would be rewarded with unique mounts, they could return to doing that or add a different 'reward shop' with something like 'bloodied trophy crystals' (red ones) that are awarded to the top players and allow purchase of items from the new shop, including mounts, minions, and glamour. The currency would ideally only be given in a small amount, or even just a singular one so that players would continue to participate in ranked the following season as I imagine items would only get added to the shop with major patches and those last two seasons.

In conclusion, I firmly believe that ranked crystalline conflict, the players who engage in it, and the potential players who would do so with suitable encouragement; would stand to benefit from a new and better reward system. As it stands now, there is little more motivation to play ranked than to chase spots on the leaderboard, which is not anymore rewarding than the other lodestone leaderboards such as Grand Company, Frontline, or Free Company leaderboards.