Baseball has to fill the minor leagues...With the Rangers that's 5 leagues (AAA, AA, High A, Low A, Rookie). That's 125 positions without even counting any of the 25 on the major league roster. Take 150 and subtract football's 53 and you'll need an extra 97 guys just to have a normal roster.
Now, take the NFL, whereas the 7 guys (Give or take a few) you draft this year, about 5 will hold a roster spot in September. In baseball you're lucky if your picks see the major leagues in 2 years (Our first round 2002 pick is in AA, last year's pick is set to see Arlington in 2006 at the earliest).
Also, most teams only draft 40 rounds (You can stop anytime) and of those about 50% will sign with you. So really you're only landing about 20 new guys.
How about this for a stat - out of those 40, if you get 2 guys to have careers in the major leagues, it's a successful draft.