It takes less vertical space because it reuses the (mostly empty) title bar.
The title bar is supposed to be a mostly empty expanse that you can grab with a mouse. Now it's littered with controls, and I can hardly bring windows to focus or move them around without accidentally searching something or confirming something.
In that case you don't need discoverability for something you set up yourself.
It's also very fun to play with when using the Wobbly Windows effect, you can stretch them in different ways depending on where exactly you picked the window up from.
Resizing takes grabbing an edge though.
"less vertical space" so let's have a hamburger menu on a desktop screen. Right next to the window close button.
"less vertical space" so let's have a tiny search icon right next to the select button
"less vertical space" so let's have search consistently in the left corner, no in the middle, no to the right
"less vertical space", so let's have tabs, buttons, icons, and hamburger menu in one row. There's no space for the actual title or little space to drag the window? But THERE'S LESS VERTICAL SPACE ENJOY
hamburger menu on desktop should be abolished