Why do English VA struggle to pronounce names that begin or end with Ryu or Ryo?

The letters in Japanese that are usually spelled with an R in roman letters represent a phoneme that English doesn’t have; it’s in between r, l, and d. VAs whose native language does not include this phoneme may find it difficult to make that sound because of lack of practice, and because they consciously or unconsciously approximate it with the nearest phonemes that they’re used to.