Usually poor mash efficiency is caused by the following:
1) poor crush
2) poor sparging technique
3) wort stratification
4) recipe calculation
Of course, if you are accustomed to getting 75% efficiency and you copy a recipe that claims 80% you won’t hit the specified OG.
Malts do play into this. This is another reason to find a base malt that works for your system and stick with it. I won’t specifically name my preferred base malt but it rhymes with Bahr.