Okay it's simple, this is the best variety show I've ever watched.
I've gotten into lots of long running variety shows but this is the first that that I didn't get annoyed of or bored of after a period of time.

Once they changed to the school concept, the show was only going up from there. (Although I do enjoy the old eps as a fan of the show).
Every single person in this cast is CRUCIAL to what knowing bros is. At first I didn't like a good number of the members, but then I realized they are all extremely funny in different ways and they all make jokes off of each other which is why having the seven of them is so important.
This the ONLY show I have seen that can make the show extremely entertaining even when the guests they have are boring. They also have no limits on this show which makes it much more fun to watch. The jokes they make are jokes that definitely would not fly on other shows, and their use of informal language also makes the show much more fun for both the viewers and for the people on the show (as they've said themselves).
The games they play with guests are always extremely entertaining and fun as well.
The occasional skits are always great too. Some of the members are extremely good at ad-libbing and it makes the skits extremely fun to watch.
Even when you don't know who the guests are, the cast does a great job at promoting them and making the episode funny.  (I've learned so much through this show it's insane).
The producers are also very funny and enjoy filming the show with the cast, which once again makes the show more entertaining.
The editing team also does an amazing job with editing in really weird animations for certain things that happen in the show.

Overall, the combination of the concept, the cast, and the staff, is genuinely amazing and results in episodes that are extremely memorable and still funny when watching them over and over again.