My guess is that it takes time to research what universal behavior users expect from a component based on examples in existing software. It's universal, so it has to work with everyone: mouse, keyboard, touch; large monitors and tiny phones; screen readers; and users with motor difficulties. And existing components may not have even thought of all of these cases.

For example, they've recently introduced the Interest Invoker API for tooltips on hover. Tooltips are ubiquitous, but they still haven't settled on what the trigger is for non-mouse users. Long press for touch is far less discoverable than mouse hover, for example.

Maybe it's a good thing they didn't rush this design three decades ago, when virtually all users were on desktop.