It is a physical thing. A Betta's mouth is just not made for flakes, although they may try one, the pellets and bloodworms go down easier.
Inari, if you are feeding your little female as much as it sounds like she is going to get sick. The Betta meal is:
Pellets 3 or 4 pellets twice a day (that is all or they will be SO constipated)
or if you happen to have a Betta who only wants bloodworms the meals are
Worms 6 to 7 worms twice a day ( same as above about the constipation)
This means pellets OR worms; NOT both.
Rose