It's a thing that I actually really dislike. A literal copy of the first games. They should have taken a bit liberty in some parts, like allowing trade with Hoenn from the beginning, or at least when you reach Bill. Having to play the whole game without any Johto or Hoenn Pokemon was boring. I have RedBlueYellow for that. HGSS handled this issue way better. In FRLG you can't even evolve Pokemon who's evolution wasn't in the original games. I had to carry Golbat until Elite Four which it trying to evolve after each level, only to say it stopped.
Basically it's the same thing all over again and it was extremely boring. I'd rather replay my RBY games than play FRLG. Thankfully they learned their lesson in HGSS.
EDIT: Now that I've beaten the E4 and went to Sevii Island, I have to say that the islands are quite boring. It's just visiting some random locations with the same encounters. I hoped for some new Pokemon, and not Pidgey/Meowth/Spearow combination on ALL seven. This is easily my least favorite game in the series. I'll play it just for the sake of Pokedex and trade with RSE.