It is part of what is fascinating about the bounty system just4me has set up. Normally I would agree with you about IF defense (Wills and Raines combined for about 80 bad plays, defined as (errors + minus plays) - (plus plays)). But they also provided about 250 net steals. That's a pretty good ROI.
Another way to look at this team: the offense was incredibly efficient. They hit very few doubles (only 4 teams hit fewer); very few HR (only 3 teams hit fewer), drew 433 walks (league average was 473), and had a below average team OPS (.702 compared to .706).
Yet they still finished 4th in runs scored, with 855. League average was 760, and the highest scoring offense was 895.
I didn't keep track of (and am too lazy to go back and look at it in detail) but I bet we played > .750 ball against teams with D+/D/D- arms. Just checking one team that platooned a pair of D- catchers, we went 10-2 against them. In those 12 games we stole 118 bases and were caught 9 times.