Why can I not assemble conduit around cable, but must pull it after assembly?
Guaranteed Reusability
If you run the wire as you are putting together the conduit, there is a possibility, unless you are truly careful about all the details, that you could end up in a situation where your initial set of wires are perfectly fine, but that pulling them out to replace them - or more likely pulling in new wires (out is &quot;easy&quot;) will run into unexpected problems. If you assemble everything first then the first time you pull wires through you will find and fix any problems. Plus you will be more careful (especially if you don't do this kind of thing every day) to play by the rules so that you will be able to pull that first set of wires without a problem.
Remember, conduit serves three different functions:

Physical protection
Grounding (for metal conduit)
Ease of use - i.e., add or replace wires as needed

The first two, which obviously are the &quot;safety&quot; issues, will be the same whether you do conduit-then-wire or conduit-with-wire. But for the 3rd, it can make a big difference.