I have been a member of several unions and I know what I'm talking about.
You can disagree if you want, but I am speaking from real life experience.
I have been part of the legal counsel to several Hollywood guilds/unions, and have participated in the production of multiple Hollywood and non-Hollywood productions. Like you, I was also a member of a non-Hollywood union (while I was in the public sector), though that experience is irrelevant to the topic at hand.
The intended legal requirement can be very different from the way it’s practiced on the ground.
My own attempts to break-in + friends’ experiences shows a clear pattern: the guilds gatekeep, almost arbitrarily, and creates environments primed for abuse.
Perhaps the legal, corporate side of the guilds should realign with the reality on the ground and change this. That is, if this is an undesirable state of affairs.
It sounds like you and your friends tried to get hired as crew onto jobs for which you have no experience, because if you guys did have the experience you would already be union members and you would be swamped with work or offers. (The thresholds are pretty low. I'm one production away from being a member of several unions and I'm trying very hard to avoid that since it would limit my ability to work on non-union productions).
Most jobs don't hire people without experience without someone vouching for them. Why would you think that Hollywood would be different? They don't know you from Adam and from their point of view there are millions of other people just like you that are willing to put in the time and effort to start at the bottom instead of trying to skip a few rungs.
If you want to work in film, start at the bottom (i.e., meaning as an assistant or an extra) or work non-unionized productions (generally, low-budget or student films).
I’ve been a member of SAG (as a child, but still!) and the WGA (as an adult). The systems are imperfect. They are also significantly better than productions with no guild affiliation.
This is not simply false, this is the typical FUD spread by people who have no idea how guilds or unions actually work.
SAG does not prohibit non-union actors in SAG-covered productions. In fact, appearing in a SAG-covered production is how one qualifies for membership into SAG.
SAG sets minimum thresholds for pay, benefits, and rights. Actors are free to negotiate better packages if they have the leverage for it. Most don't, which is why the actor-waiter meme is a thing for people hoping to get cast into a SAG-covered role. As someone who has appeared as a background actor in a SAG-covered production: SAG minimums are significantly higher than non-SAG pay, at every level.