In my experience, the only people who find all-caps easier to read are the sort of people that trace the line with their finger and move their lips while doing so.
Anyone that can read at a reasonable speed reads the shapes of most words, rather than looking at each letter individually. THIS IS PRACTICALLY IMPOSSIBLE TO DO WHEN THE TEXT IS ALL IN CAPITAL LETTERS.
From my own experience, a lot of that is just what someone is accustomed to. I suspect the difference would be less if almost everything we read was in uppercase.