> Starting a video in most browsers is pretty expensive (it usually loads up various GPU features for hardware video decoding).
OTOH it might be cheaper (relatively) on phones as they can offload the work to hardware components and ramp CPU down (or avoid ramping it up).
On some old and buggy machines, that might cause the browser to crash too.
Not something Google wants to risk for a doodle - that's why all non-trivial doodles require a click to load.