Currently the HBM 2 chips that AMD uses come in 4GB size and in order to get to 16GB, AMD had to take four HBM 2 chips. Launching a card with 16GB might sound like overkill but it was an engineering rather than a business decision. Radeon Instinct MI50 card based on 7nm is 16GB and AMD didn’t want to set aside a huge engineering team to create a custom 8GB version of that card that would be cheaper and more appropriate for healthy gaming market margins. AMD could have disabled 8GB, but it would still end up paying for the whole 16GB HBM 2.