Explain to me how anything from the noughties can be 'Trek'. The entire point is that it is not. I hardly expect starfleet captains to wear the naval uniform from Generations day-to day. XD
The point is that this is casual wear. And casual-wear can, and should, be anything. We just don't tend to see any of the main characters out of their uniforms in case there's an emergency and they have to be called to their station.