Yes, that's right, we can ask questions in the Thread "Development & Technical Discussion" & "Wallet software" but if there is a special child board then the discussion about bitcoin core will be neater and it will be easier to find references about bitcoin core.
I suspect that before there was a child board, perhaps the board was intended for discussions about bitcoin core, but after there was a child board, it would be fairer if bitcoin core also had a special child board.
Sorry, I just realized that "Bitcoin Technical Support" is a board specifically for bitcoin core, Because the description is "Questions regarding issues with Bitcoin Core, nodes, the Bitcoin network, transactions, and addresses"