Why is there a 7 day waiting period between chapters?

Since the game began in Oct 2017, developers have always released only 1 new chapter per week (with some breaks for holidays and between volumes), and they do not intend to change that. They compare it to a TV episode released every week.

Yes, when you are caught up to developers, you must wait for them to release a new chapter every Thursday. To make the wait less, some players play just one new scene a day. You can still increase your level beyond that (max level 1050 until the next volume is released). Also be aware that you will only get 20 blue 1-star boxes per week with no way to get additional, so use them wisely.