That's not an easter egg, that feature probably increased the number of likes in videos since it made the button easier to spot when users were looking for it (

That's not an easter egg, that feature probably increased the number of likes in videos since it made the button easier to spot when users were looking for it (which is when it is mentioned on videos). So that sweet engagement KPI is positively impacted and Youtube's CRO/experiment/Ab testing team gets their cookies. There are probably various small tweaks like this in the UI.