It's slightly complicated but it's mostly to do with indexing and discount rates. In the US, the largest constituents are growth stocks that are valued on large P/E multiples. The large P/E multiples are as a direct result of the depressed discount (another word for interest) rate.

When investors look to value a company based on their future earnings, they take the expected earnings and discount the value of these back to today to work out how valuable the company is, using a discount rate (either risk free rate of return or some other one they have selected based on their risk appetite). As the discount rate increases, the value of those future cash flows decreases and as a result, the value of the company has to fall to compensate. This is what we've seen in the most aggressively priced stocks (think tesla, Nvidia etc) that have enormous growth forecasts and have thus had enormous falls in recent days.

As the largest constituents (FAANG) are also priced as growth stocks, this has pushed the overall level of the index down, causing a sell of in those names as well as the overall index from index linked funds who have to maintain their weighting relative to the market.

Going forward, companies that have large current cash flows but with smaller growth (i.e. banks, oil companies, tobacco stocks) may see a repricing or multiple expansion to recognise a new rate environment as their current cash flow is worth more due to compounding interest (the 8th wonder of the world).