There are several reasons why kids would choose to go to a junior college out of high school as opposed to a D-1 school. As mentioned before, a player can be drafted out of a juco after his freshman, and/or sophomore years; at a D-1 (or any 4 year) you can only be drafted after your junior or senior season, or third year out of high school (i.e. redshirt, 2 playing seasons).
Also, jucos generally have more scholarships to offer, whereas D-1s have 11.7 scholarships per year, and very, very, few kids get "full rides," to Division 1 schools; jucos could have several players on full rides. So, a player could go to a juco, get drafted twice, not like his position in the draft, and go on to possibly get drafted one or two more times at a university.
Another plus to a juco is the regulations regarding fall practices/practice time is much less restrictive than at D-1s, which gives a player much more time to work on weaknesses and improvement is probably more likely in many cases. As for quaility of jucos in Texas, Grayson, San Jac, Blinn, North Central Texas, Navarro, and several others all have great programs with Grayson, Blinn, and San Jac usually being able to compete with most D-1s, for sure. Nationally, Yavapai, Seminole State, Meridian CC, Maple Woods, Connors State, and a few others are really strong as well.