Interpreting the standard error from emmeans - R

I am using the emmeans package to run post-hoc analysis on linear mixed models. The results provide what I would expect except for the standard error. I run the example code provided in the documentation:

warp.lm <- lm(breaks ~ wool*tension, data = warpbreaks)warp.emm <- emmeans(warp.lm, ~ tension | wool)warp.emm# wool = A:#   tension   emmean       SE df lower.CL upper.CL# L       44.55556 3.646761 48 37.22325 51.88786# M       24.00000 3.646761 48 16.66769 31.33231# H       24.55556 3.646761 48 17.22325 31.88786# # wool = B:#   tension   emmean       SE df lower.CL upper.CL# L       28.22222 3.646761 48 20.88992 35.55453# M       28.77778 3.646761 48 21.44547 36.11008# H       18.77778 3.646761 48 11.44547 26.11008# # Confidence level used: 0.95

I can't understand how the SE values are all the same, when the means (and everything else) are completely different? What do these SE values actually represent? Thank you