It's not as though SE is choosing for the process to take time. It takes time because the servers are in the midst of a rather intensive process to log you out. Until that process is complete, it could cause data corruption to log you back in when you'd only been half-way logged out.

Now, maybe there are ways for SE to speed up the process, and if so, that would certainly be good.

I do think there should be an immediate logout and close option instead of always putting you back in the launcher. But that wouldn't allow logging back in any more quickly. The server still needs to complete your logout before you can log in. But if you're done with FFXIV for the day, it could let you move on to other things while it does so.