Doing average for image collections changed spatial resolution in GEE

I tried to calculate the averaged map for a satellite product in a month using GEE, but after I exported the result, I found the spatial resolution was changed into 1 lat/lon deg, and the native resolution is ~500m.

var mcd = ee.ImageCollection("MODIS/006/MCD43A3").filterDate('2004-01-01', '2004-01-31').select('Albedo_BSA_shortwave')

var clim_mcd = mcd.reduce(ee.Reducer.mean());

var myScale1 = mcd.toBands().projection().nominalScale().getInfo()
var myScale2 = clim_mcd.projection().nominalScale().getInfo()
print(myScale1)
print(myScale2)

code

and the results show

How can I fix this issue and export the averaged image result with the native resolution?