Your first sentence is wrong for many scenarios and is meaningless without a time interval. Over a period of 10 years the risk historically is absolutely higher from inflation than a total market mutual fund.

If people were good at sweeping excess balances into their investments I think this idea would be less appealing. But for a variety of reasons, many perfectly rational, people like having a nice cushion in there. It feels safe. Long term, it isn’t. These guys should lean into that in their marketing.

My checking account (and the checking account of the majority of Americans) isn’t measured in intervals anywhere close to 10 years.

The reason perfectly rational people like having a cushion in their checking account is that rent payments don’t care about 10 year historic trends; they’re just due when they’re due.

I’m sure there’s a decent collection of people here with enough disposal income that the idea of just having all their capital invested sounds lovely. But we’re inside a bubble here.