This is because nobody can say how many people are needed to develop or maintain some body of software. So companies hire however many employees they can afford. When the number they can afford changes they hire more or fire some. The number of staff has pretty much nothing to do with the actual work. AI introduces another factor to the equation: it allows one person to perform N times as much softy-work as before. So even if you have no idea how many people you need (as always, see above) you do know that you can get by with 1/N.