In a sandbox, there are no episodes or different routes. It's multiple parallel story lines. If you want episodes and different routes. Make a VN with options and choices, in which case I would love to bring this game back from the trash bin. But until that happens. This game stays in the trash bin.
Beside that. Missing content also happens in VN's when they are multi routed.
And yes. This is far from the only game, which try to fit a VN story line into the sandbox format. And yes. They all fail and become grind games.
One of the few sandbox games that actually is a proper sandbox game is Love & Sex Second Base
https://f95zone.to/threads/love-sex-second-base-v23-9-0e-andrealphus.13488/
Another one that works from a format point of view is Club Detention
https://f95zone.to/threads/club-detention-v0-064-hotfix-3-yorma86.120015/post-12005050
Both games works because they have multiple parallel story lines, that only sometime crosses and very seldom is mutual exclusive. When they cross in most cases one of the story lines has to wait while the other one catches up, after which the both progress in different directions again. The choices you make doesn't end one in favor of another.