The issue here is one of ownership and licensing. As a creator, you own the copyright in anything you create that can be copyrighted unless is it a work for hire. If SLR were to hire someone as an employee or on a contract that stated it was work for hire, then they would own the copyright in the script, yes. But this depends on scripters being willing to work under such an arrangement. Why would you, if you can make more money by retaining ownership for yourself? Your skill is in demand, people want your content, that's the very definition of opportunity. As long as scripting remains a difficult skill to obtain, scripters will be in the driving seat.
An example from my own field of work: you may have heard of Salesforce. It's a CRM platform that businesses use to handle customers. It has its own software development platform based around a proprietary language. If you want to do custom development on top of Salesforce you need developers who can use this language and platform. It's not particularly hard to pick up, but there aren't many people who have the skill because frankly it's boring work, so it's super expensive to hire people to do it. And it's essentially impossible to hire people to do it as permanent employees because they can make so much more money doing it as a contractor. You can hire someone inexperienced and train them up, but once they acquire the skill to a high enough level, they realise they can make much more money as a contractor and they leave to go contracting.
Right now, scripting is in this position. High demand, low supply, and the creator is firmly in control. It won't always be this way. Eventually, AI tools will reach the point where it can be largely automated, and then it'll become a commodity skill and companies like SLR will be able to have junior staff who just take care of the auto-scripting bot, and they will own all the rights, and scripts will just be available for all content by default.
I'm sure SLR could negotiate either assignment of copyright or 'perpetual and irrevocable' licenses for scripts. Then they could not be taken away by the creator later. I imagine the $500 script offer probably works that way. But if I were a script creator in demand I would not agree to that if I could retain my rights and improve my bargaining position. The time investment required is too great to give those rights away for a one-time payment, unless it's a very big payment.
SLR has more scripts available than any other place by a country mile. They obviously got there by offering deals that attracted scripters. If the price of that was agreeing a deal that allows the scripter to walk away later because that's what they insist on, then that's the deal you have to do, because the alternative is not having the script at all. Yeah, it sucks for us that scripters can withdraw their scripts later, just like it sucks for us that studios can withdraw their content from the platform. I'm sure SLR doesn't like it either. But they are not the ones in control here.
