I may be wrong about this, but I believe I heard there is a rule in place where if a baseball signee is a two sport athlete, the MLB team has the option to spread out the signing bonus over a few years, so for Senquez, I think it's possible that this over $1M figure was spread out over 4 years or so, and there may have been stipulations to it as well. I don't think it was directly comparable to the typical signing bonus.
Still, I probably would've been gone for that kind of money even with stipulations and with it spread out. Obviously he really wanted to go to school though. Some guys are just like that. I remember Alan Horne turning down big money as a first rounder out of high school so he could come to Ole Miss. I got the chance to meet him, and I asked him point blank why he turned down the money, and his answer was that he wanted to go to law school. Baseball wasn't his major motivation. He was an odd character. He ended up transferring to Florida and never got the big payday for baseball later. I'm not sure what he's doing today or if he ended up pursuing the law school thing. Point being, not everyone is driven just by money or sports.
Same could be said for Greg Hardy. He had first round potential, but he talked a lot about wanting to start a greeting card business. Football just wasn't his first priority. He enjoyed art more. Another odd and frustrating character.