Part of it comes down to fact that it's harder to fire people.
Another part of it is that bureaucracies end up becoming dominated by people who serve the survival of the bureau (and it's budget) at the expense of its actual mission.
Another part is that government agencies are just not as easy to hold to account - with a private business your customer can often take their business elsewhere (and if they can't, well, the government just might be the reason for that). In theory the democratic process should hold these agencies accountable, but the democratic process is more indirect than voting with your feet. And there is generally a tendency to resist democratic influence (otherwise the agency would become political).
There are probably many other reasons as well.
Yes, what I was getting at! Developers can coast and never be forced to improve or learn new skills. very very difficult to be fired.
I’m sure it exists, but the meme seems overblown. From what I’ve seen, government is more frugal than the private sector day to day, the main difference is that the government ends up supporting unprofitable programs and has additional burdensome regulations that drive up costs (eg buy American)