A standard 2050 lifecycle fund allocation like LifePath 2050 index funds will generally have a very tiny allocation to cash (~1% in this example) because as you mention the target date is far out and cash is not a long term investment. However, for LifePath dynamic funds
Allocations are flexible to capture opportunities in changing markets.
If you look at the "portfolio" section of the link you gave you will notice that the "dynamic" fund has taken an ~8% position in "Net Derivatives," which means they are likely using derivatives to short some of the exposure in their portfolio likely because they believe that certain markets are overpriced. They hold ~8% cash to fully cover these short derivatives plus ~1% cash mainly to cover trading (like the index fund) for a total of ~9% cash.
It's often cheaper and easier to use derivatives to take short positions especially if you expect your short position to be temporary. Say, if you think you will take profits immediately in a market correction. Funds are often required to hold cash to cover short positions to avoid situations where they may be hurt by margin calls.
It's tough to know exactly what Blackrock is doing with these derivatives but if you have access to the fund's Quarterly Commentary it likely talks about what short position they are taking and why they believe it is the correct move for their fund at this time.