Well, the main reason is that nobody liked the first design. The mint was a new venture, and they were simply finding their way.
There was an outburst after the S-1 came out, so they switched from the "Chain Reverse", viewed as a symbol of shackles (limiting) rather than freedom, to the Wreath.
But still, nobody really liked the Lady Liberty, so they went with the French Liberty Cap - much like the one Franklin used on the Libertas Americana, and people seemed okay with that, so that's what they stuck with for the obverse for a few years.
Minting coins then was a very different thing than it is now, and the mint had plenty of detractors. There were many people against the US coining it's own money. The pay was meager and the hours were long - but then again, that's kinda how it was in every profession but for the elite back then.
Still, it was a very sensitive subject, and the people's voice carried a great deal of weight. As then is now and always, nobody likes the current coinage.