Hit the nail on the head with this. Engineering started off as rules of thumb and best practice. SE is an emerging field. In 50 - 100 years i think we'll have it down.

Also regular constraints don't apply to software that normally would in construction fields. Gravity and mass and other real constraints are not present in program construction. Time and complexity are massive issues, but imagination and the mental model of a process is the usual barrier. Just think about anything web scale, (google docs?) its impressive for 'meh' engineering.