Earthworms are more nutritious, more filling, do not hop around, don't stink, and they do not bite. Plus, worms aren't escape artists unlike crickets. Crickets can also bite your frog while worms cannot. Never heard of crickets being hard to digest, but I do know that meal worms are and would not feed your frog meal worms.

Some pacmans can be finicky when it comes to what they like. I would keep trying to encourage him to eat the worms. If they are big you can cut them up and serve them with feeding tongs. Dubia roaches are also better than crickets. One dubia roach is the equivalent to five crickets.