Probably to make it acceptable for the new generation, unaccusomed to things like 'leveling' and 'money farming'.
But seriously, the newer 'generation' RPGers are probably used to relatively simple RPGs in the difficulty department.
And for a short summary of the changes in the GBA version:
-MP System. Instead of using a certain maximum number of spells a spell level, you use MP like the later games.
-Max Level 99.
-Easier time leveling up (not including the Provoka Peninsula, of course.
-Added in extra items to replace crappy items in chests, like Phoenix Downs, Ethers, Elixirs, and so on.
-Items are also much less expensive (yes, even that one set of armor in the Elf Village).
-Save anywhere. Yep, even in dungeons.
-B Button dash. Can also configure it to always be active.
-Bonus dungeons and broken equipment/items.
-You have the option of forgetting a spell, in the original, your spell selections were permanent.
-Warp pad in the Temple of Chaos. Travelling two-thousand years into the past was never so easy!
-Although enemy stats are amped up to counter this (for example, Chaos has 20,000 HP, that should be a good example), this doesn't necessarily make them harder. It just doesn't make them jokes.
That's about it...but at least, the translation is nice, although Origins' translations were fine as they were (well, except the funky names for FFII).
Final Fantasy II also was tweaked, but not to the extreme as FFI. For example, the famous attack/cancel bug was taken out, but skills/weapons level up tolerably enough so that it isn't really necessary to use it. They also took out the second Blood Sword in the basement of Fynn Castle to make the final boss not so easy.