Halving is not a magical event that means the price of Bitcoin will increase before or after that. This is something that simply reduces the block reward by 50%, and in the long term that means less new mined coins on the market.
What's the reason for the price drop is in the domain of speculation, so you can pick what seems most realistic to you.
- Bakkt failed to meet the expectations of many people, so when they see price will no go up, they start to sell.
- Price was holding too long at the same level ($10k), and as always if there is no power for up, it needs to go down.
- FUD about some big mining farm is burn/hashrate is down for 40%.
It's actually very easy for some people to manipulate the crypto market, just by buying/selling big amounts of coins in a short period of time. The reason is always profit, I don't think this drop is an exception either.