I guess it would have made too much sense (and the same goes for Koresh and Weaver) to wait until the guy goes out in town and just pick them up out in the open...
For those opining about using different tactics, the arrest warrant is usually issued along with a search warrant. The evidence gathered by the search warrant can often make or break the case.
Arresting people outside their home allows time for the destruction of evidence by friends and family. Also there may be no reduction of risk simply by grabbing the primary target. Other people in the house can carry just as much as risk to the officers.
And it should be noted that you can get smoked approaching a guy on a sidewalk just as easily as you can going into his house.
Hitting a house always carries risk but it is a "one and done" and is usually a better option when viewed from a big picture perspective.
