GMS majorly gets all the general major contents/updates from KMS. Reg server users have been asking for the meso cubing ever since it was implemented in KMS a year and a half ago. We always leave these suggestions and feedback regarding meso cubes in official Maplestory's Discord server's "Suggestion and Feedback" channel but it never gets addressed.
There was even recent post in Reddit asking what prevents Heroic/Reboot from playing Interactive and a lot of comments also mention cubing as a major hindrance from playing Interactive. Paying $20-$25 for 10 cubes is ridiculous.
Recent patches about Familiars in all regions, tradable cash outfits are all what Heroic/Reboot users have been mainly asking for these as priority and they got it while reg user's priority are always ignored and not even addressed.
It's been over a year since this meso cube should have been implemented according to the KMS to GMS update schedule. Give us the meso cubing update already.