It has been recently announced that DC aren't planning to join their movie universe to the shows already running, which is a really bad idea on their hand, because it would really help them, and here are 5 reasons why.
They Can Expand Their Universe Quicker
Marvel is way ahead of DC in movies, I mean they have made seperate movies for all of the Avengers WITH sequels plus the Avengers movie itself, with an upcoming sequel.
The only movie DC have really done is Man of Steel with an upcoming movie "Batman vs. Superman: Dawn of Justice" which is supposedly including five characters (Batman, Superman, Aquaman, Wonder Woman and Cyborg) already. With the TV Show, Arrow and the upcoming Flash, DC can definitely expand their universe by making solo movies for these characters, or even a team-up movie much like the Flash/Green Lantern team-up movie announced. They have also announced a Shazam movie, so on my count we already have 8 characters, including Green Lantern and Shazam. (And if you like, you can include Black Canary from Arrow, making 9)
Imagine having 7 (since MoS was Superman's solo movie) solo movies released by DC!? If you think about it, we theoretically can get a JL movie b7 2020. With BvS in 2016, we could have Shazam in 2017 and most probably a MoS2 in 2018, with a possible Batman solo in the same year, which gives about 3 years (if the actors go straight from solo movies to JL movies) to make the movie, plus we could fit in about 3 seasons of each show from 2015-2018, making the third of those seasons available for preparing the titular characters for the events in the JL movie.
It Gives Us A Lot More Plots For Seasons of 'Arrow' and 'Flash'.
Yes, another reason is that is gives their shows a lot more plots for seasons of Arrow and Flash. The events of Man of Steel and the upcoming BvS can impact the TV shows. A few plots could be:
Arrow Version: Oliver Queen is at home with his family when the power goes out and the TV flutters on and Zod's transmission from Man of Steel comes on.
Flash Version: Barry is in S.T.A.R. Labs with his colleagues and the same thing happens.
Version 2: Since the events of MoS, everyone from all around the globe look to Superman for guidance and help now, rendering heroes like the Arrow and the Flash useless and unwanted. By the end of the season/s Batman and Superman have fought each other publicly, showing that they are incapable of helping people when they are too busy fighting each other, which makes people look up to heroes like the Flash and the Arrow & co.
More Money For DC
This one is obvious. Yes, Batman vs. Superman and the Justice League movie will definitely gross a s*it ton of money, but what about the TV Shows? Once people have seen the Arrow and the Flash on the big screen they are going to want more, but they may have to wait 2 or more years for that, so there's no better way than to look to the TV Shows of these characters! This overall gets more views, more selling merchandise (although the seasons of the shows would mostly be downloaded)
Gives Fans a Chance to See the Small Screen Characters on the Big Screen
On the Small Screen, the effects, although good, are nowhere near as good as Big Screen effects. Did you see Man of Steel? Amazing effects! Imagine seeing the Arrow in a fist fight with someone on the Big Screen with modern day CGI? I mean he doesn't have superpowers but jese!
And what about people like the Flash? He could have some really amazing running scenes, and not to mention the fist fights he could have with people. Imagine a race between Superman and Flash on the big screen? Like in that one episode of Smallville except a trillion times better effects.
The Fans Would Just Love DC, Possibly Spawning More Shows AND Movies
I mean come on! You'd have Superman fans, Batman fans, Arrow fans, Flash fans, and not to mention the massive amounts of people who don't even read the comics! Hell, you'd even have a few die hard Marvel fans at the cinemas to see it.
I think if they did this right, the JL movie could earn more money than the Avengers. Plus, as I said above, the TV shows would get a lot more fans, and the JL movie could even spawn a lot more TV Shows, such as an Aquaman show, a Cyborg show and even a Wonder Woman show.