dakar has some good ideas but all you can do is encourage owners to take care of the health of the world. Unfortunately the only thing that's in it for them is a sense of civic duty and sportsmanship.
If a world is out of minor leaguers, it's because many of the owners are hoarding money for free agents, international or otherwise. Having healthy minor league teams requires a small amount of managing them, and a margin of cash that might otherwise be spent going after higher impact returns. So many owners do things like not signing any draftees other than major prospects, not promoting players so they retire early, and maintaining minimum roster sizes so players get injured. At the start of a season they simply sign up the cheapest players they can find from any source, assign rosters, then never look at them again. You will see teams with 10-120 records, box scores like 25-3. I've seen a first baseman used as a starting pitcher racking up 80+ starts. And then you will see that same kind of team signing an IFA with a 36.4 million dollar bonus.
On my teams with healthy minor league systems, promoting from within, I almost never have to sign minor league free agents at the start of a season unless I need to fill specific defensive positions like SS or C. But this is because I never play the 20 mil plus IFA game.