Alphabet Inc.’s deeper dive into the U.S. financial system shouldn’t come as much of a surprise. Technology giants have found a way into all corners of people’s lives; the latest plan to offer consumers new forms of bank accounts is simply one of the final frontiers.

The puzzling part of Alphabet’s expansion of Google Pay is why Citigroup Inc. is a willing participant in Silicon Valley’s invasion of Wall Street’s turf.

Last week, Bloomberg News and others reported that Citigroup and a California credit union were Alphabet’s initial partners for a venture that would offer checking accounts through Google Pay.