What you say is true if you make a game with GB Studio 3. It just came out within the last week though. All of the GB Studio games that have been created so far were on version 1 or 2 so the porting would be migrating to the new version which is a pretty big task.
Hello,
I created a fork a GB Studio 2 that export natively game in pocket file.
https://github.com/BestPig/gb-studio#analogue-pocket-export
I don't know if migrating a game from 1.0 to 2.0 breaks stuff, so maybe only works for game made with the 2.0. If you have any issue with it, don't hesitate to contact me.