It stands to reason that the team who procured the prospect has a better read, feel, and intel on him than the team trading for him. Sure there's the occasional Doyle Alexander for John Smoltz trade, but the reality is the team trading the major leaguer is typically trying to salvage something for an asset set to depart and is essentially collecting lottery tickets. The further away from free agency an existing major league asset is, the better the lottery tickets should be (Soto). But the majority of trades are for half season rentals and thus the majority of the prospects exchanging hands are further away from being sure things.
It's equally hard to find many deals where the Brewers traded the rental major leaguer for lottery tickets and found anything of consequence. But when it hits, it's pretty darn great (Lind for 3 tickets, one of who was Freddy Peralta).
For the most part the trades where more sure thing prospects get dealt are prospect for prospect trades and deals where the major leaguer getting sent out has multiple years of control. If you're letting teams poach a prospect from you that is a future star, for say a Josh Bell, you're internal scouting is a mess.