Scrip gear for each expansion likely requires you to unlock its respective "sanctuaries" to access the Scrip Exchanges there.
Heavensward (max lv 60): Foundation/Idyllshire
Stormblood (max lv 70): Kugane/Rhalgr's Reach
Shadowbringers (max lv 80): Crystarium/Eulmore
Endwalker (max lv 90): Old Sharlayan/Radz-at-Han
Dawntrail (max lv 100): Tuliyollal/Solution 9

Thus, as you're lv 75, it makes sense to require access your lv 70 endgame gear at Rhalgr's Reach.

As soon as you have access to Tuliyollal though, I'd spend purple scrips on Grade 11 materia instead of Scrip Gear though. Scrip Gear is OK, but they're not that great...

Personally, I usually prefer crafting out my whole set of gear instead of using Scrip Gear for every expansion. I always recommend skipping the lv 70/80/90 crafted gear, as they're endgame sets and usually very mat-heavy. In contrary, the crafted lv 71/81/91 are great to have, as they are easy to make, but are nearly as strong as the endgame gear from the previous expansion. Crafting new items in HQ from your crafting logs also provides a huge amount of EXP anyway.

Also, Scrip Gear sets' accessories, pants and boots usually provide pathetically few CP. For crafted accessories, you can meld with some very cheap CP materia (during leveling). The extra CP you can get from this allows more flexibility in rotations, provides much more power than Control or Craftsmanship, and also more fun in the crafting game. When you switch accessories/pants/boots, you can just retrieve the CP materia, and re-meld to any new gear. Nothing is wasted.