IMO they eat more museli because they pick out the yummy bits and leave the not so yummy but often healthier bits!
It's not really a big deal if they don't eat many pellets, they don't *need* commercial piggy food in their diet, as long as they're getting their fibre and vit. C needs from hay (80% total diet minimum) and fresh veg.
I've always found excel to be pretty high quality, and fairly decent stuff - I saw a big change in my pigs when I started feeding them on it, compared to the poorer diets they'd been on before they came to me.
As others have mentioned, there is the blackcurrant and oregano version, and there's also other good quality brands, I believe Science Selective is supposed to be the "top" brand.
At the end of the day, if your pigs are getting their nutritional needs met through their hay and veg, it's not such a bad thing if they chose not to eat too many pellets.
I wish I could get mine to eat less - they're currently on diets!