2Prick,,
Your cross-trainer workout of 15 minute sessions 4 or 5 times per week, demolished your gut for you.
But there is a massive ingredient: diet.
Diet is everything. Your Macros (protein/carb/fat) ratio, type of carbs you intake, and your total caloric intake.
Plus, your metabolism.
What you eat before this cross-training could influence the results also.
Good on you, but each individual has different routines that work for him/her.