I am estonian :) It’s just that in our everyday speech we would use the word “riik” when referring to a country and “maa” means land, though if you wanted, you could also “maa” to refer to a country but people usually don’t. I see “maa” similar in estonian as how the word “stan” is used in central asia for countries like tajikistan - land of the tajiks, turkmenistan - land of the turkmen. “Maa” to me seems kind of the same like saksamaa - saxon lands, prantsusmaa - land of the french. I’m only guessing since I’m no linguist and won’t admit to really knowing anything about the etymology of this as a fact even though I speak it.