Banning the players for life would be an insane leap. Open up that can and the MLB would have a much bigger PR problem than they already do. The league would start circling the drain as former players start pointing fingers left and right and all over - then the MLB would have to be consistent and ban many many more players and coaches for things they did years in the past.

As is, they probably approached this the right way. Make examples of the Astros (and probably the Red Sox) to discourage this moving forward - but to bring out a retroactive hammer and be mired in constant investigations would be a disaster.