Since they sign their share of $10K LA prospects, at some point they may simply feel the remaining prospects are more trouble than they're worth (probability of success is so low it doesn't justify coaching resources, etc.).
And there are probably a few where the demand so exceeds the expected value that they don't want to set a precedent (hi, we're idiots, demand whatever you want).
I think some teams make the decision that LA spending plus associated costs (sufficient scouts to identify 2nd and 3rd tier prospects who aren't easily scouted) isn't worth the return.
The alternative today is to go all in with an expanded scouting group (which will cost millions, not so much salary but travel and lodging, Panama, Columbia, Venezuela, Brazil, Mexico, DR . . .adds up).
Sure, they should have overspent back in the day, but water under the bridge.
If they're trading for allocations and spending on the scouts required to identify all viable candidates, then they're pretty much "all in."