Tesla have done a lot of vertical integration, but for other manufacturers there's a lot of common electronic components. Stuff like headlamps (even if it's a different plastic housing the board will be the same basic design), door locks, infotainment, dashboard displays where there's little reason to significantly reengineer them for an EV.

Not only is the majority of an EV the exact same components as an ICE car, but the electric car industry has been using off the shelf components for decades.

Tesla buys plenty of products from them, including things like electric steering assist.

Bosch wants to stay relevant for longer than ICE cars after all, and a lot of these components were developed for ICE cars anyway.

For the powertrain, sure obviously and absolutely.

But e.g. why have different electric window motors, wiper motors, turn signal solenoids etc etc?