They'd give just as much incentive to owners to not sign suspected players as they give players (allegedly) for not taking PEDs.
As it stands now, it's a one-way street. There is no downside to signing a player who might be using PEDs. If he gets caught, great! No need to pay him. If he doesn't, great! We'll be the beneficiary of all those great numbers!
But if MLB was really interested in cracking down on PEDS, which they are not, they would require the team of a player who failed a drug test to pay the equivalent of that player's salary to all the teams in in their division who didn't have a player test positive.
This way, if a player tests positive, money comes out of the player's pocket, money comes out of the owner's pocket, and the competing teams benefit. If this system were in place today, i wonder if the Mets would have been so willing to pay Bartolo Colon $20 million over 2 years?