Except that the Pentagon, which actually plans for future wars, says that we don't need it and that they don't want it. And the Pentagon also has no contingency planning for actually implementing a draft. The US military already spends more than the next 10 militaries combined (or some such). We have long-distance deployment capacities that no other nation can come close to matching. And we have ocean borders to provide security that no other nation has.
And if they ever actually did do some new draft, the actual paperwork process of implementing a draft that the selective service does would be by far the easiest and most trivial part of the entire process that could be most quickly put together if they were starting from scratch. All the other parts would be MUCH more complicated and difficult.
1. The Military would have build a large number of new bases from scratch where they could house and train hundreds of thousands or millions of draftees. Over the past 50 years we have closed down and surplused all of the old bases that were previously used for that purpose as the military has shrank. For example, the Presidio in San Francisco is now a park. Where are you going to house and train millions of new draftees?
2. The military would have to equip a bunch of new divisions or squadrons or fleets which would mean building massive new quantities of tanks, trucks, planes, helicopters, guns, ships, etc. During WW2 they could do that by flipping assembly lines for Ford and GM into tank plane production. Modern weapons are far more complicated and expensive. We aren't just going to equip a bunch of infantry battalions by issuing them uniforms and sticking an M1 rifle into their hands like WW1 or WW2. That type of war is long over.
3. The military would have to create from scratch the logistics capacity to supply and transport all these new divisions and squadrons. So thousands of new cargo planes and ships that don't exist, hundreds of new supply depots and warehouses that don't exist, etc. etc.
So in the unlikely event that there ever would be some new draft, it would take the military years to gear up to where they could actually accommodate waves of millions of new draftees. Ramping up some new electronic registration system for young men and women to register for possible conscription is going to be the least of their worries. Your average tech company like Google could build that capacity in a day.
The military isn't keeping the selective service because they want to be ready for an emergency. Congress just doesn't have the political will to do away with it because there would inevitably be politicians that would grandstand and demagogue any attempt to get rid of it. So it just plods along decade after decade doing nothing but creating unnecessary busy work and wasting taxpayer dollars.