Form responses are stored in multiple sheets or tab because a new sheet/tab is created in your form’s spreadsheet after you make an edit to your form. This is automatically done to preserve your data integrity and prevent data from being overwritten.
Currently, this behavior cannot be prevented or turned off. It is helpful to avoid confusion of your received responses/data also. For example, if your form had 12 fields, during an edit you removed 3 fields to bring the fields down to 9 and also changed the field labels/questions, inserting form responses into the same sheet will break your form columns and cause misunderstanding of incoming data.