My first thought was that this was done with consideration for mobile phones, since many higher-end models use 120 Hz displays, but Ladybird does not seem to support mobile for now.

> Websites using requestAnimationFrame now render at up to 120Hz on supported hardware

But the phrasing of it about "can now" suggests to me that this may simply be a performance issue too. They changed it from 60 to 120. Perhaps in the future they can go from 120 to 144 or even 240.