How come in pokemon heartgold, you don't have berries from the regular pokemon gold?

Question

Like the mint berry or the poisoncure berry or the gold berry?

Answer 1

Because there was a small berry overhaul in Gen III, to make the Pokeblock feature more appealing.

When Heartgold/Soulsilver came out, they couldn't confuse their current audience by reverting the Pecha berries back to PSNcurberry, Cheri Berry to PRZcurberry, etc. It would be too confusing.