Thank you for your feedback.
DDT was developed using TWINE's chapbook format, and I thought its automatic saving feature was effective in heightening the tension of the game. However, I do agree that having the option to save manually would be more convenient. To implement this, I would need to switch from the chapbook format to another format, which would require a complete overhaul of the game.
Crashing is a slightly different issue from whether or not you can save anywhere. It is caused by major changes to internal game variables that conflict with the variables stored in the auto-save, and this cannot be avoided even if you can save anywhere.
Fundamentally, the reason is that I, as the developer, have made major changes to make the game more interesting, sacrificing compatibility with previous versions.