No it’s not. It’s the nature of insular groups. Teams spend a LOT of time together in practice. Colds and flus rip through locker rooms. Their insular nation generally helps them avoid introducing a bug, just because they don’t spend enough time away from the team facilities to get a lot of exposure, but once the seal gets broken BAM. First somebody gives it to the strength and conditioning coach or his assistants, then everybody has it.
Pro athletes should have been dropping out like flies due to seasonal flu then.