There are likely legal reasons why they take such a cautious approach. Once you're baptized, you can be df'd. They don't want disfellowshiped people pleading ignorance and/or possibly suing.
Also, they don't want people bearing the name of "Jehovah's Witness" while still steeped in some practices that are going to bring "reproach" upon the Organization.
Their approach is overly-cautious and tedious, but just going ahead and baptizing people would be a major headache for them, even if it's more in tune with what the 1st Century Christians did.