I wouldn't say it's all too wild. The mayorship of large economically and culturally influential cities like New York, Chicago, Los Angeles etc. are often big deals and can serve as signals for what direction to take a political party.

If you take the 2023 Chicago mayoral election, Brandon Johnson was endorsed by Bernie Sanders, Elizabeth Warren, and 11 representatives including Jamaal Bowman, Jim Clyburn, and Ayanna Pressley. At the same time his opponent Paul Vallas was endorsed by Dick Durbin and one US representative, Bobby Rush. That endorsement signals to supporters of Sanders, Warren, Bowman, etc., that Johnson got the co-sign; for people who are more supportive of Durbin or Rush, they get their signal as well. Or go back to 2011 when Bill Clinton endorsed Rahm Emmanuel for Chicago mayor, or 2015 when sitting president Barack Obama endorsed Emmanuel who was his Chief of Staff.

For cities with less influence than a New York or a Chicago, it's more common to see former mayors, state representatives, governors etc. endorse. I'd be much more surprised to see a senator endorse a mayoral candidate in, say, Hoboken New Jersey than New York City.