Maybe they did all believe what they were told "we've checked it and its all fine"
I don't think that's so far fetched.
If an employer, potentially a legal expert and your agent all tell you that it's good, and other players tell you that it's totally above board and never been a problem, then your likely to accept it too.
It's not as clear cut as brown paper bags full of cash.
Investments in a business for safeguarding a players future post-rugby can definitely be spun in a way that makes it sound like the player isn't getting any benefit in the short term.
I suspect the players all felt they were getting a good deal, but also probably had been convinced it was totally fine