Quoted By:
Q: Why wasn't the Battle Frontier in the remakes?
A: This question is connected with my previous answer. We didn't put the BF in ORAS for this very reason.
Interviewer's note: In short he means that they didn't include the BF because only a very small part of the players would have fully appreciated and made use of this feature; nowadays players get bored and frustrated more easily and they aren't interested in things that are so demanding/challenging.
Meanwhile, in the actual anime the Battle Frontier continues to exist with Satoshi going there and winning a tournament and it’s image being drawn similar to its look in Emerald. Really makes you think.